Encoder

ABSTRACT

An encoder is configured for detection of rotational movement of a rotatable shaft in relation to a part of a machine, and a method is provided for generating a reference signal by an encoder.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Application No. 1200406-5,filed in the Kingdom of Sweden on Jul. 2, 2012, which is expresslyincorporated herein in its entirety by reference thereto.

The present application claims the benefit of U.S. Provisional PatentApplication No. 61/713,801, filed on Oct. 15, 2012, which is expresslyincorporated herein in its entirety by reference thereto.

FIELD OF THE INVENTION

The present invention relates to an encoder apparatus. The presentinvention also relates to a method of operating such an encoderapparatus, and to a computer program product for causing an encoder toexecute functions.

BACKGROUND INFORMATION

In many industrial applications there is a need to monitor the movementof a movable part. Such monitoring requires the delivery of an encoderoutput signal indicative of the movement, or indicative of the positionof the movable part.

It is conventional to provide an encoder apparatus in which the encoderoutput signal is generated in dependence on a detected magnetic field. Amagnetic encoder may include a magnetic scale that can be installed on arotatable shaft of a machine. U.S. Patent Application Publication No.2010/0207617 describes an incremental encoder for detection of themovement of a shaft including a scale having a series of spaced magneticmarks mounted on the circumference of the shaft. A read head is mountedon another machine part so as to pass along the scale, the read headincluding a first set of detectors 16-1 for sensing the scale marks, andgenerating a pulsed signal in response to rotational movement of theshaft and scale in relation to the read head. In order to be able togenerate an encoder output signal indicating not only incrementalmovement of the shaft, but also providing a position output signal, acounter is used for counting the pulses of the pulsed signal, thecounter value being indicative of the position. In order for the countervalue to reflect the position of the shaft within a single revolution,it is conventional to provide the magnetic scale with a magneticreference marker. In this manner, the reference marker is used forgenerating a reference signal once per shaft revolution in response tothe magnetic reference marker passing a separate second set of referencesensors 16-2 provided in the read head, as described in U.S. PatentApplication Publication No. 2010/0207617. Providing a separate referencemarker next to the scale requires additional space, which may not beavailable, as pointed out in U.S. Patent Application Publication No.2010/0207617. To address this problem, U.S. Patent ApplicationPublication No. 2010/0207617 describes providing the reference mark byfurther magnetizing the scale in a region of one of the existing polepitches so as to produce a reference signal. The further magnetizationextends across only a part of the width of the scale, covering less thanhalf of the width, so that the incremental signals may be readundisturbed, according to U.S. Patent Application Publication No.2010/0207617.

SUMMARY

Example embodiments of the present invention provide an improved encodersystem.

According to an example embodiment of the present invention, an encoder,for detection of rotational movement of a rotatable shaft in relation toa part of a machine, includes a scale device for attachment to acircumference of the shaft, and the scale device having a width and alength. The scale device includes a first magnetic scale patternincluding a plurality of magnetic pole elements provided with a firstpredetermined division in the direction of the length so as to generatea first magnetic field pattern at a first distance from a surface of thescale device. A signal generator is provided for mounting on the machinepart, the signal generator including a housing. The signal generatoralso includes a first output terminal suitable for providing an encoderoutput signal indicative of a relative change in position between thesignal generator and the scale device. The signal generator includes asecond output terminal suitable for providing a reference signalindicative of a rotational position of the shaft. The signal generatorfurther includes a first magneto-electric transducer head having a firstmagneto-electric transducer adapted to generate a first electric signalin response to detection of the magnetic field pattern so that the firstelectric signal varies periodically in dependence on the first magneticfield pattern such that the variation exhibits a first wavelength, whichdepends on the first predetermined division when the firstmagneto-electric transducer moves along the first magnetic scalepattern. The signal generator also includes a second magneto-electrictransducer head having a second magneto-electric transducer adapted togenerate a second electric signal in response to detection of the firstmagnetic field pattern so that the second electric signal variesperiodically in dependence on the first magnetic field pattern such thatthe variation exhibits the first wavelength dependent on the firstpredetermined division when the second magneto-electric transducer movesalong the first magnetic scale pattern. The signal generator alsoincludes a first signal processing unit, which includes: a first deviceadapted to generate a periodically varying first digital signal independence on the first electric signal such that the variation of thefirst digital signal exhibits the first wavelength when the firstmagneto-electric transducer moves along the first magnetic scalepattern; and a second device adapted to generate a periodically varyingsecond digital signal in dependence on the second electric signal suchthat the variation of the second digital signal exhibits the firstwavelength when the second magneto-electric transducer moves along thefirst magnetic scale pattern. The scale device includes at least one gapbetween ends of the first magnetic scale pattern. The signal generatorfurther includes an analyzer adapted to generate a scale gap indicatorsignal in dependence on an analysis involving the first digital signal,or an analysis involving the second digital signal and/or a comparativeanalysis involving the first digital signal and the second digitalsignal. Moreover, the signal generator includes an output signalproducer adapted to produce the encoder output signal in dependence onthe first digital signal and the second digital signal, and the outputsignal producer is adapted to produce the reference signal in dependenceon the scale gap indicator signal.

This arrangement provides for a reference signal at least once perrevolution of the rotatable shaft, while eliminating the need to makethe scale so wide as to allow for the provision of a separate magneticreference mark. Hence, whereas U.S. Patent Application Publication No.2010/0207617 describes to reserve almost half of the width of the scalefor a separate magnetic reference mark, which would appear to require arather wide scale when also requiring the first set of detectors 16-1 toread the incremental signals undisturbed from the other half of thewidth, the width of the scale device described herein may be madenarrower. The encoder output signal may be an incremental signal whichis indicative of a change in position. The encoder output signal mayalso be indicative of a rotational position of the shaft 20.

Moreover, the housing of the signal generator may also be made smallwith respect to the physical extension in the direction parallel to theaxis of rotation of the shaft, since, in contrast to the U.S. PatentApplication Publication No. 2010/0207617, this eliminates the need for aseparate second set of reference sensors positioned so as to read themagnetic reference marker from one half of the scale width whileallowing the first set of detectors to read the incremental signalsundisturbed from the other half of the scale width.

Moreover, it is noted that large shafts, such as, e.g. shafts having adiameter of 50 cm or more, may have an axial play, i.e., the shaft mayinadvertently move during operation, in a direction parallel to the axisof shaft rotation, which also is the direction of the width of the scaledevice. If such movement occurs, the position of the magneto-electrictransducer head may also be shifted in relation to the width of thescale. The arrangement described herein allows for mounting of thesignal generator including the magneto-electric transducer head on themachine part, so as to allow the axial play to move the scale device adistance substantially equal to half the width of the scale device,while maintaining magneto electric detection, when the signal generatorhas been mounted at an optimum position.

The fact that the magnetic scale pattern generates a magnetic fieldpattern at a first distance from a surface of the scale device, incombination with the ability of the magneto-electric transducers togenerate electric signals in response to detection of the magnetic fieldpattern may render a non-contact detection. In effect, no movable partof the encoder is in physical contact with any other part of theencoder, thereby, e.g., rendering an encoder which is free frommechanical wear. Hence, the configuration described herein may providean encoder having a very long, or even unlimited, service life. Thelongevity feature of this non-contact detection is particularlyadvantageous in connection with the use of the encoder in machines whichare difficult or cumbersome to maintain, such as a wind power station.In a wind power station, the encoder may be mounted to detect themovement of the rotating shaft at the high altitude of a wind powertower, making it difficult for maintenance personnel to reach theencoder for maintenance purposes.

According to example embodiments, the scale device 30 may be made of aflexible band, such as, e.g., a bendable steel band, provided with anopenable locking device so as to allow the flexible band to be openedsuch that it may be placed at a desired measuring path position on theshaft. When positioned at the desired measuring path position on theshaft, the locking device of the flexible scale band may be closed andlocked so as to attach it to the desired measuring path position on theshaft. The locking device may then be used as the gap portion of thescale device.

According to example embodiments, the scale device may include adividable scale ring. The inner diameter of the dividable ring maysubstantially correspond to the outer diameter of a shaft to which thedividable scale ring is intended to be attached. The dividable scalering may then have at least two openings so as to allow the ring to bedivided in at least two parts. Hence, an opening of the dividable scalering may be provided with an openable locking device so as to allow thedividable scale ring to be opened such that it may be placed at adesired measuring path position on the shaft. When positioned at thedesired measuring path position on the shaft, the locking device of thedividable scale ring may be closed and locked so as to attach it to thedesired measuring path position on the shaft. The locking device maythen be used as the gap portion of the scale device.

According to example embodiments of the present invention, an encoder,for detection of rotational movement of a rotatable shaft in relation toa part of a machine, includes a scale device for attachment to acircumference of the shaft, the scale device having a width and ameasuring path length. The scale device includes a first magnetic scalepattern including a plurality of magnetic pole elements provided with afirst predetermined division in the direction of the length so as togenerate a first magnetic field pattern at a first distance from asurface of the scale device. A signal generator is provided for mountingon the machine part, the signal generator including a housing. Thesignal generator further includes a first output terminal for providingan encoder output signal indicative of a relative change in positionbetween the signal generator and the scale device, and a second outputterminal. The signal generator includes a first magneto-electrictransducer head having a first magneto-electric transducer adapted togenerate a first electric signal in response to detection of the firstmagnetic field pattern so that the first electric signal variesperiodically in dependence on the first magnetic field pattern such thatthe variation exhibits a first wavelength, which depends on the firstpredetermined division when the first magneto-electric transducer movesalong the first magnetic scale pattern. The signal generator alsoincludes a second magneto-electric transducer head having a secondmagneto-electric transducer adapted to generate a second electric signalin response to detection of the first magnetic field pattern so that thesecond electric signal varies periodically in dependence on the firstmagnetic field pattern such that the variation exhibits the firstwavelength dependent on the first predetermined division when the secondmagneto-electric transducer moves along the first magnetic scalepattern. The signal generator further includes a first signal processingunit including: a first device adapted to generate a periodicallyvarying first digital signal in dependence on the first electric signalsuch that the variation of the first digital signal exhibits the firstwavelength when the first magneto-electric transducer moves along thefirst magnetic scale pattern; and a second device adapted to generate aperiodically varying second digital signal in dependence on the secondelectric signal such that the variation of the second digital signalexhibits the first wavelength when the second magneto-electrictransducer moves along the first magnetic scale pattern. The scaledevice includes at least one gap between ends of the first magneticscale pattern. The signal generator moreover includes an analyzeradapted to generate a scale gap indicator signal in dependence on ananalysis involving the first digital signal, or an analysis involvingthe second digital signal and/or a comparative analysis involving thefirst digital signal and the second digital signal. Still further, thesignal generator includes an output signal producer adapted to producethe encoder output signal in dependence on the first digital signal thesecond digital signal, and the scale gap indicator signal.

This arrangement may provide a scale gap indicator signal, therebyproviding an absolute position signal which can be reset, e.g., once pershaft revolution, in dependence on the scale gap indicator signal, whileeliminating the need to make the scale so wide as to allow for theprovision of a separate magnetic reference mark. Hence, this arrangementallows for the provision of an absolute position signal output, usingthe provision of a gap in the scale pattern, to achieve the advantagesmentioned above in connection with the example embodiment that alsoprovides a reference signal.

The scale device may be adapted for attachment on a shaft having adiameter of more than 50 cm.

The first magneto-electric transducer head may be arranged at apredetermined distance from the second magneto-electric transducer head,within the signal generator housing, such that the signal generator ismountable so that, in operation, at least one of the first and secondmagneto-electric transducer heads will be positioned so as to detect thefirst magnetic field pattern.

The gap may include at least a portion of the measuring path lengthlacking the first magnetic scale pattern.

The gap may have a gap width, which is dependent on a distance betweenthe ends of the first magnetic scale pattern.

The predetermined distance between the first magneto-electric transducerhead and the second magneto-electric transducer head may be longer thanthe sum of the gap width and at least one first predetermined division,in the case that the first and second magneto-electric transducer headsare magneto-resistive transducer heads.

The predetermined distance between the first magneto-electric transducerhead and the second magneto-electric transducer head may be longer thanthe sum of the gap width and at least two first predetermined divisions,in the case that the first and second magneto-electric transducer headsare Hall sensor transducer heads.

The configuration described herein may ensure that there is a transitionperiod covering a distance of at least one wave length for switchingfrom relying on the latter transducer head to relying on the foremosttransducer head in connection with a gap cross-over. Hence, thisconfiguration allows for both of the latter transducer head and theforemost transducer head to simultaneously detect at least one fullelectric signal wave length, i.e., a first predetermined wavelength λ₁,after the foremost transducer head having crossed the gap, and beforethe output signal is switched over to be generated in dependence on theforemost transducer head.

The first magneto-electric transducer head may include a first laggedmagneto-electric transducer adapted to generate a first lagged electricsignal in response to detection of the magnetic field pattern so thatsaid first lagged electric signal varies periodically in dependence onthe magnetic field pattern such that the variation exhibits the firstwavelength which depends on the first predetermined division when thefirst lagged magneto-electric transducer moves along the magnetic scalepattern. The first lagged magneto-electric transducer is positioned inrelation to the first transducer such that, in operation, the firstlagged electric signal varies at a first lag in relation to the firstelectric signal when the shaft rotates in a clockwise rotationaldirection, and such that the first lagged electric signal varies at asecond lag in relation to the first electric signal when the shaftrotates in a counterclockwise rotational direction, the second lag beingdifferent from the first lag.

The second magneto-electric transducer head may include a second laggedmagneto-electric transducer adapted to generate a second lagged electricsignal in response to detection of the magnetic field pattern so thatthe second lagged electric signal varies periodically in dependence onthe magnetic field pattern such that the variation exhibits the firstwavelength which depends on the first predetermined division when thesecond lagged magneto-electric transducer moves along the magnetic scalepattern. The second lagged magneto-electric transducer is positioned inrelation to the second transducer such that, in operation, the secondlagged electric signal varies at a first lag in relation to the secondelectric signal when the shaft rotates in a clockwise rotationaldirection, and such that the second lagged electric signal varies at asecond lag in relation to the second electric signal when the shaftrotates in a counterclockwise rotational direction.

The first lag may substantially correspond to a quarter of the firstwavelength, and the second lag may substantially correspond to threequarters of the first wavelength.

The first lagged magneto-electric transducer and the firstmagneto-electric transducer may be Magneto-Resistive Transducers, andone first wavelength may be generated by the distance of one firstpredetermined division.

The first lagged magneto-electric transducer, having a direction ofsensitivity, may be positioned at a geometrical distance from the firstmagneto-electric transducer, also having a direction of sensitivity. Thefirst magneto-electric transducer and said first lagged magneto-electrictransducer may be arranged such that their respective directions ofsensitivity are substantially parallel, and the first lag may depend onthe geometrical distance.

The geometrical distance may be a quarter of the first predetermineddivision.

The configuration described herein may render the first lag to become aquarter wavelength when the magneto-electric transducers aremagneto-resistive transducers.

The first lagged magneto-electric transducer, having a direction ofsensitivity, may be positioned in geometrical proximity to the firstmagneto-electric transducer, also having a direction of sensitivity. Thefirst magneto-electric transducer and the first lagged magneto-electrictransducer may be arranged such that there is a geometrical anglebetween their respective directions of sensitivity, and the first lagmay depend on the geometrical angle.

The configuration described herein may render the first lag to beindependent of the first predetermined division of the scale device.Hence, the first magneto-electric transducer head having the firstmagneto-electric transducer and the first lagged magneto-electrictransducer may be used together with different scale devices havingmutually different first predetermined divisions. Likewise, the secondmagneto-electric transducer head, having the second magneto-electrictransducer and the second lagged magneto-electric transducer, may bemade in the same manner as described for the first magneto-electrictransducer head. In this manner, a flexible signal generator may beachieved, thus rendering usability with various magnetic scale deviceshaving mutually different first predetermined divisions.

The geometrical angle may be substantially 45 degrees.

The configuration described herein may provide for the first lag of themagneto-electric transducer head to become a quarter wavelengthirrespective of the first predetermined division distance.

The geometrical proximity may be selected such that the firstmagneto-electric transducer and the first lagged magneto-electrictransducer are arranged at substantially the same location, such as, forexample, with substantially no distance between the first laggedmagneto-electric transducer and the first magneto-electric transducer.

The first lagged magneto-electric transducer and the firstmagneto-electric transducer me be Hall sensor transducers. One firstwavelength may be generated by the distance of the two firstpredetermined divisions.

The geometrical angle may be substantially ninety degrees.

The first signal processing unit may include a Field programmable gatearray circuit adapted to simultaneously process the first digital signaland the second digital signal.

The periodic variation may be arranged as a periodic oscillation.

The signal generator may include a device adapted to detect a signaledge in the periodically varying first digital signal, and a firstcounter for generating a first count value indicative of a number ofdetected signal edges so that the first count value is indicative of afirst rotational position estimate of the scale device in relation tothe signal generator.

The signal generator may include a device adapted to detect a signaledge in the periodically varying second digital signal, and a secondcounter for generating a second count value indicative of a number ofdetected signal edges so that the second count value is indicative of asecond rotational position estimate of the scale device in relation tothe signal generator.

The signal generator may be adapted for mounting on the machine part sothat, in operation, the first magneto-electric transducer is positioneda second distance from the surface of the scale device, the seconddistance being substantially equal to the first distance or smaller thanthe first distance.

The signal generator may include a housing adapted to enclose the firstmagneto-electric transducer head and the second magneto-electrictransducer head. The housing may include a wall for facing the machinepart and a front wall for facing the shaft. The front wall may have aphysical extension in a direction parallel to the elongation of theshaft, a physical extension in a direction orthogonal to the elongationof the shaft, and a concavely curved shape in the direction orthogonalto the elongation of the shaft. The first magneto-electric transducerhead may be positioned in relation to the second magneto-electrictransducer head such that, in operation, at least one of the first andsecond magneto-electric transducer heads will be positioned so as todetect the first magnetic field pattern.

According to example embodiments of the present invention, a signalgenerator, for mounting on a machine part and for co-operation with ascale device, includes: a housing; a first output terminal for providingan encoder output signal indicative of a relative change in positionbetween the signal generator and the scale device; a second outputterminal; a first device adapted to generate a periodically varyingfirst digital signal such that the variation of the first digital signalexhibits a first wavelength when the signal generator moves along afirst magnetic scale pattern of the scale device; and a second deviceadapted to generate a periodically varying second digital signal suchthat the variation of the second digital signal exhibits the firstwavelength when the signal generator moves along the first magneticscale pattern of the scale device.

The first device is adapted to also generate a periodically varyingfirst lagged digital signal such that, in operation, the first laggeddigital signal varies at a first lag in relation to the first digitalsignal when the shaft rotates in a clockwise rotational direction, andsuch that the first lagged electric signal varies at a second lag inrelation to the first electric signal when the shaft rotates in acounterclockwise rotational direction, the second lag being differentfrom the first lag. The second device is adapted to also generate aperiodically varying second lagged digital signal such that, inoperation, the second lagged digital signal varies at a first lag inrelation to the second digital signal when the shaft rotates in aclockwise rotational direction, and such that the second lagged digitalsignal varies at a second lag in relation to the second digital signalwhen the shaft rotates in a counterclockwise rotational direction.

According to example embodiments of the present invention, an encoderincludes the signal generator.

The encoder may include: a first position value estimator for generatinga first position value estimate in dependence on at least one of theperiodically varying first digital signal, and the periodically varyingfirst lagged digital signal; and a second position value estimator forgenerating a second position value estimate in dependence on at leastone of the periodically varying second digital signal, and theperiodically varying second lagged digital signal.

The first position value estimator may include a first counter moduleadapted to generate a first count value by counting periods of the firstwavelength in dependence on at least one of the periodically varyingfirst digital signal, and the periodically varying first lagged digitalsignal. The first position value estimator may be adapted to generatethe first position value estimate in dependence on the first countvalue. The second position value estimator may include a second countermodule adapted to generate a second count value by counting periods ofthe first wavelength in dependence on at least one of the periodicallyvarying second digital signal, and the periodically varying secondlagged digital signal. The second position value estimator may beadapted to generate the second position value estimate in dependence onthe second count value.

The first position value estimator may be adapted to generate the firstposition value estimate in dependence on a count value, which isgenerated by counting periods of the first wavelength of theperiodically varying first digital signal, of the periodically varyingfirst lagged digital signal, or of a periodically varying signalgenerated in response to one or both of the periodically varying firstdigital signal and the periodically varying first lagged digital signal.The second position value estimator may be adapted to generate thesecond position value estimate in dependence on a second count value,which is generated by counting periods of the first wavelength of theperiodically varying second digital signal, of the periodically varyingsecond lagged digital signal, or of a periodically varying signalgenerated in response to one or both of the periodically varying seconddigital signal and the periodically varying second lagged digitalsignal.

The first position value estimator may include a first arctan functiongenerator module adapted to generate a first electrical angle value independence of the periodically varying first digital signal, and theperiodically varying first lagged digital signal, so that the firstelectrical angle value is indicative of a position of a firstmagneto-electric transducer head within a distance corresponding to onefirst predetermined wavelength. The first position value estimator maybe adapted to generate the first position value estimate in dependenceon the first electrical angle value. The second position value estimatormay include a second arctan function generator module adapted togenerate a second electrical angle value in dependence of theperiodically varying second digital signal, and the periodically varyingsecond lagged digital signal, so that the second electrical angle valueis indicative of a position of a second magneto-electric transducer headwithin a distance corresponding to one first predetermined wavelength.The second position value estimator may be adapted to generate thesecond position value estimate in dependence on the second electricalangle value.

The first position value estimator may include a first rotationaldirection detector module arranged to generate a first rotationaldirection signal indicative of a current direction of rotation of theshaft. The second position value estimator may include a secondrotational direction detector module arranged to generate a secondrotational direction signal indicative of a current direction ofrotation of the shaft.

The first counter module may be adapted to adjust the first count valuein dependence on the first rotational direction signal, and/or thesecond counter module may be adapted to adjust the second count value independence on the second rotational direction signal.

The first position value estimator may be adapted to generate the firstposition value estimate in dependence on the first electrical anglevalue and/or the first rotational direction signal and/or the firstcount value. The second position value estimator may be adapted togenerate the second position value estimate in dependence on the secondelectrical angle value and/or the second rotational direction signaland/or the second count value.

The encoder may include a signal treatment module, having: a deviceadapted to generate a first head position value which is indicative of aposition of a first magneto-electric transducer head; and a deviceadapted to generate a second head position value which is indicative ofa position of a second magneto-electric transducer head.

The encoder may include an analyzer adapted to generate a scale gapindicator signal in response to detection of a deviation between themagnetic field pattern as sensed by a first magneto-electric transducerhead and the magnetic field pattern sensed by a second magneto-electrictransducer head; and/or in response to detection of a change in themagnetic field pattern as sensed by a first magneto-electric transducerhead or the magnetic field pattern sensed by a second magneto-electrictransducer head.

The encoder may include an analyzer adapted to generate a scale gapindicator signal in response to detection of a change in the magneticfield pattern as sensed by a first magneto-electric transducer head by aphase error signal switching from a state indicating no phase error to astate indicating the detection of a phase error.

Providing such a phase error signal may be used for indicating that thecorresponding detector head is just entering a gap in the scale at theposition visited by that detector head.

The encoder may be adapted to store the current first head positionvalue, as a scale edge position value for the detector head.

The encoder may include an analyzer adapted to generate a scale gapindicator signal in response to detection of a change in the magneticfield pattern as sensed by a first magneto-electric transducer head by aphase error signal switching from a state indicating a phase error to astate indicating no phase error.

Providing such a phase error signal may be used for indicating that thecorresponding detector head is just leaving a gap section and enteringthe scale at the position visited by that detector head.

The encoder may include an analyzer adapted to generate the scale gapindicator signal in dependence on a comparative analysis involving thefirst digital signal and the second digital signal, and/or a comparativeanalysis involving the first position value estimate and the secondposition value estimate.

The analyzer may be adapted to generate the scale gap indicator signalin dependence on a comparative analysis involving the first positionvalue estimate and the second position value estimate. The analyzer maybe adapted to generate a Both_On_Scale signal indicating that both thefirst magneto-electric transducer head and the second magneto-electrictransducer head are in a position to detect the scale when both of thefirst position value estimate and the second position value estimateagree about the detected position or the detected amount of movement.The analyzer may be adapted to generate a signal indicating that onemagneto-electric transducer head is not in a position to detect thescale when the first position value estimate and the second positionvalue estimate disagree about the amount of movement.

The analyzer may be adapted to generate a First_Off_Scale signalindicating that the first magneto-electric transducer head is not in aposition to detect the scale when the second position value estimateindicates a certain degree of movement whereas the first position valueestimate indicates less movement or substantially no movement.

The analyzer may be adapted to generate a value indicative of adifference in detected movement, the difference value indicating adifference between the second position value estimate and the firstposition value estimate.

The output signal producer may include a synchronization module forsynchronizing the second position value estimate and the first positionvalue estimate so as to render the difference value to a predeterminedvalue, such as, e.g., zero.

The analyzer may be adapted to read the difference value in response tothe Both_On_Scale signal, and the analyzer may be adapted to store thedifference value as a value indicative of a width of a gap between scaleedges.

This arrangement may allow the encoder to measure the width of the gap,as experienced by the magneto-electric detector heads.

The analyzer may be adapted to generate the scale gap indicator signalin response to the difference value reaching a predetermined value.

The analyzer may be adapted to generate the scale gap indicator signalin response to the difference value reaching a predetermined value,e.g., corresponding to a certain ratio of the gap width value.

The analyzer may be adapted to generate the scale gap indicator signalin response to the difference value reaching a predetermined value,e.g., being substantially half of the gap width value.

An output signal producer of the encoder may be adapted to generate theoutput reference signal in dependence on the scale gap indicator signal.

The analyzer may be adapted to generate the scale gap indicator signalin response to the First_Off_Scale signal.

The first lag may substantially correspond to a quarter of the firstwavelength, and the second lag may substantially correspond to threequarters of the first wavelength.

The first lagged magneto-electric transducer and the firstmagneto-electric transducer may include magneto-resistive transducers,and one first wavelength may be generated by the distance of the onefirst predetermined division.

The first lagged magneto-electric transducer, having a direction ofsensitivity, may be positioned at a geometrical distance from the firstmagneto-electric transducer, also having a direction of sensitivity. Thefirst magneto-electric transducer and the first lagged magneto-electrictransducer may be arranged such that their respective directions ofsensitivity are substantially parallel, and the first lag may depend onthe geometrical distance.

The geometrical distance may be a quarter of the first predetermineddivision. Thus, the first lag may become a quarter wavelength.

The first lagged magneto-electric transducer, having a direction ofsensitivity, may be positioned in geometrical proximity to the firstmagneto-electric transducer, also having a direction of sensitivity. Thefirst magneto-electric transducer and the first lagged magneto-electrictransducer may be arranged such that there is a geometrical anglebetween their respective directions of sensitivity, and the first lagmay depend on the geometrical angle.

This arrangement may render the first lag to be independent of the firstpredetermined division of the scale device. Hence, the firstmagneto-electric transducer head having the first magneto-electrictransducer and the first lagged magneto-electric transducer may be usedtogether with different scale devices having mutually different firstpredetermined divisions. Likewise, the second magneto-electrictransducer head, having the second magneto-electric transducer and thesecond lagged magneto-electric transducer, may be made in the samemanner as described for the first magneto-electric transducer head. Inthis manner, a flexible signal generator may be achieved, thus renderingusability with various magnetic scale devices having mutually differentfirst predetermined divisions.

The geometrical angle may be substantially 45 degrees. Thus, the firstlag of the magneto-electric transducer head may become a quarterwavelength irrespective of the first predetermined division distance.

The geometrical proximity may be selected such that the firstmagneto-electric transducer and the first lagged magneto-electrictransducer are arranged at substantially the same location, such as, forexample, with substantially no distance between the first laggedmagneto-electric transducer and the first magneto-electric transducer.

The first lagged magneto-electric transducer and the firstmagneto-electric transducer may include Hall sensor transducers, and onefirst wavelength may be generated by the distance of the two firstpredetermined divisions.

The geometrical angle may be substantially ninety degrees.

The periodically varying first digital signal and the periodicallyvarying first lagged digital signal may be generated by a firstmagneto-electric transducer head when the first magneto-electrictransducer head moves along a first magnetic scale pattern. The analyzermay be adapted to generate the scale gap indicator signal in dependenceon an amplitude analysis of the periodically varying first digitalsignal and the periodically varying first lagged digital signal usingthe fact that they are substantially quadrature signals when the firstmagneto-electric transducer moves along a first magnetic scale pattern.

Since the two signals are substantially quadrature signals, thePythagoras relation stating that Sqr(A)+Sqr(B) is constant, leads to theeffect that the sum of the squares is substantially constant when thefirst magneto-electric transducer head moves along a first magneticscale pattern. However, when the first magneto-electric transducer headpasses over a scale edge the sum of the squares becomes lower, which maybe due to the magnetic field becoming weaker in the gap portion of thescale. This may be used for detecting an edge of the magnetic scale.

The periodically varying second digital signal and the periodicallyvarying second lagged digital signal may be generated by a secondmagneto-electric transducer head when the second magneto-electrictransducer head moves along a first magnetic scale pattern. The analyzermay be adapted to generate the scale gap indicator signal in dependenceon an amplitude analysis of the periodically varying second digitalsignal and the periodically varying second lagged digital signal usingthe fact that they are substantially quadrature signals when the firstmagneto-electric transducer moves along a first magnetic scale pattern.

The analyzer may be adapted to set a first amplitude reference value independence on the sum of the square of the periodically varying firstdigital signal and the square of the periodically varying first laggeddigital signal. The analyzer may be adapted to set a second amplitudereference value in dependence on the sum of the square of theperiodically varying second digital signal and the periodically varyingsecond lagged digital signal.

The analyzer may be adapted to generate the scale gap indicator signalin dependence on a relation between the first amplitude reference valueand the second amplitude reference value.

The encoder may include an analyzer adapted to generate a scale gapindicator signal in response to detection of a change in the magneticfield pattern as sensed by a first magneto-electric transducer head by aphase error signal switching from a state indicating no phase error to astate indicating the detection of a phase error.

Providing such a phase error signal may be used for indicating that thecorresponding detector head is just entering a gap in the scale at theposition visited by that detector head.

The encoder may include an analyzer adapted to generate a scale gapindicator signal in response to detection of a change in the magneticfield pattern as sensed by a first magneto-electric transducer head by aphase error signal switching from a state indicating no phase error to astate indicating the detection of a phase error.

Providing such a phase error signal may be used for indicating that thecorresponding detector head is just entering a gap in the scale at theposition visited by that detector head.

The first lagged magneto-electric transducer, having a direction ofsensitivity, may be positioned at a geometrical distance from the firstmagneto-electric transducer, also having a direction of sensitivity. Thefirst magneto-electric transducer and the first lagged magneto-electrictransducer may be arranged such that their respective directions ofsensitivity are substantially parallel, and the first lag may depend onthe geometrical distance.

The geometrical distance may substantially correspond to one half of thefirst predetermined division, and the first magneto-electric transducerand the first lagged magneto-electric transducer may include Hall sensortransducers.

This arrangement may render the first lag to become a quarterwavelength.

The encoder may include a signal treatment module, having a deviceadapted to generate a first head position value which is indicative of aposition of a first magneto-electric transducer head, and a deviceadapted to generate a second head position value which is indicative ofa position of a second magneto-electric transducer head.

The encoder may include an analyzer adapted to generate a directionsignal indicative of a direction of rotation in dependence on the lagvalue generated in response to signals emanating from the firstmagneto-electric transducer head, or the lag value generated in responseto signals emanating from the second magneto-electric transducer head.During a first direction of rotation, the first magneto-electrictransducer head would pass a certain position of the scale before thesecond magneto-electric transducer head passes the certain position ofthe scale. During a second direction of rotation, the firstmagneto-electric transducer head would pass a certain position of thescale after the second magneto-electric transducer head passes thecertain position of the scale.

The encoder may include a signal treatment module, which includes adevice for switching between a first state and a second state, in whichthe second head position value is relied on for the delivery of theencoder output signal during the first state, and the first headposition value is relied on for the delivery of the encoder outputsignal during the second state. The signal treatment module may beadapted to select the first state in dependence on the analyzergenerating a Both_On_Scale signal indicating that both the firstmagneto-electric transducer head and the second magneto-electrictransducer head are in a position to detect the scale when both of thefirst position value estimate and the second position value estimateagree about the detected position or the detected amount of movement,and the direction signal may indicate the first direction of rotation.

During the first state, when the direction signal still indicates thefirst direction of rotation: the signal treatment module may be adaptedto deduce, in response to the scale gap indicator signal, that the firstmagneto-electric transducer head is positioned within a gap, and thenthe signal treatment module may be adapted to maintain the first stateso that the second head position value is relied on for the delivery ofthe encoder output signal.

During the first state, when the direction signal still indicates thefirst direction of rotation: the signal treatment module may be adaptedto deduce that the first magneto-electric transducer head is positionedwithin a gap in response to the difference value reaching apredetermined value, the predetermined value being, e.g., substantiallyhalf of the gap width value; and the signal treatment module may beadapted to deduce that the first magneto-electric transducer head andthe second magneto-electric transducer head are positioned on oppositesides of the gap when the direction signal still indicates the firstdirection of rotation and the difference value has reached a secondpredetermined value, the second predetermined value substantiallycorresponding to the gap width value or to a value exceeding the gapwidth value.

The predetermined distance between the first magneto-electric transducerhead and the second magneto-electric transducer head may be longer thanthe sum of the gap width and at least one first predetermined division,in the case that the first and second magneto-electric transducer headsare magneto-resistive transducer heads. The predetermined distancebetween the first magneto-electric transducer head and the secondmagneto-electric transducer head may be longer than the sum of the gapwidth and at least two first predetermined divisions, in the case thatthe first and second magneto-electric transducer heads are Hall sensortransducer heads.

This arrangement may ensure that there is a transition period covering adistance of at least one wave length for switching from relying on thetrailing transducer head to relying on the leading transducer head inconnection with a gap cross-over. Hence, this arrangement allows forboth of the trailing transducer head and the foremost, leadingtransducer head to simultaneously detect at least one full electricsignal wave length, i.e., a first predetermined wavelength, after theleading transducer head having crossed the gap, and before the outputsignal is switched over to be generated in dependence on the leadingtransducer head.

The predetermined distance between the first magneto-electric transducerhead and the second magneto-electric transducer head may be longer thanthe sum of the gap width and at least three first predetermineddivisions, in the case that the first and second magneto-electrictransducer heads are magneto-resistive transducer heads. Thepredetermined distance between the first magneto-electric transducerhead and the second magneto-electric transducer head may be longer thanthe sum of the gap width and at least six first predetermined divisions,in the case that the first and second magneto-electric transducer headsare Hall sensor transducer heads.

This arrangement may leave room for allowing the transition, from therelying on the trailing transducer head to relying on the leadingtransducer head in connection with a gap cross-over, to take place atpositions on the scale having a more reliable a first magnetic fieldpattern than that existing at an edge of the magnetic scale pattern.Near an edge of the magnetic scale pattern, the first magnetic fieldpattern displays fringe effects that may have a negative influence onthe quality of the electric signals produced by the transducers whenthey are positioned near an edge of the magnetic scale pattern. In otherwords, the scale pattern quality of the first magnetic field pattern isbetter at a distance from an edge of the magnetic scale pattern.

The signal treatment module may have a first state and a second state.The trailing second head position value may be relied on for thedelivery of the encoder output signal during the first state, and theleading first head position value may be relied on for the delivery ofthe encoder output signal during the second state. The signal treatmentmodule may be adapted to cause switching between a first state and asecond state during a transition period, and the transition period maydepend on the distance of movement measured in terms of the firstpredetermined wavelength.

The signal treatment module may be adapted to allow the transitionperiod to extend over at least one first predetermined wavelength.

The signal treatment module may be adapted to cause the transitionperiod to be initiated when the reliable trailing second head positionvalue indicates that the trailing second head is positioned at adistance corresponding to at least one and a half first predetermineddivisions from a scale edge.

This arrangement may provide for a transition from the reliable trailingsecond head position value to the leading head position value when bothof the heads are positioned at a distance of at least 1.5*Δ₁ from theedges of the magnetic scale at the transition occurring when the headsare straddling the gap, thereby avoiding magnetic field pattern fringeeffects during the transition period. This may lead to an improvedmeasuring accuracy, e.g., since synchronization of the first and secondhead position values leads to more reliable results at a distance fromthe edges of the magnetic scale. Moreover, the next transition fromrelying on the leading head to relying on the trailing head may also beinitiated when the trailing second head position value indicates thatthe trailing second head is positioned at a distance corresponding to atleast one and a half first predetermined divisions from a scale edge,after the trailing head passage of the gap.

The signal treatment module may be adapted to cause the transitionperiod to be initiated when the reliable trailing second head positionvalue indicates that the trailing second head is positioned at adistance corresponding to at least six first predetermined divisionsfrom a scale edge.

The signal treatment module may be adapted to cause the transitionperiod to be initiated when the reliable trailing second head positionvalue indicates that the trailing second head is positioned at adistance corresponding to at least eight first predetermined divisionsfrom a scale edge.

The signal treatment module may be adapted to cause switching between afirst state and a second state during a transition period, in which thetransition period depends on the distance of movement measured in termsof the first predetermined wavelength.

The signal treatment module may have a first state and a second state.During movement, one magneto-electric transducer head may have a leadingposition and the other magneto-electric transducer head may have atrailing position in relation to the scale device. The signal treatmentmodule may be adapted to rely on the trailing transducer head positionvalue for the delivery of the encoder output signal during the firststate, and the signal treatment module may be adapted to rely on theleading transducer head position value for the delivery of the encoderoutput signal during the second state. The signal treatment module maybe adapted to cause switching between a first state and a second stateduring a transition period, and the transition period may depend on thedistance of movement measured in terms of the first predeterminedwavelength.

In this connection, the switching is not time controlled but it israther performed by a procedure that occurs during the movement of thetransducer heads.

In some instances, the signals generated by the magneto-electrictransducers may deviate somewhat from an ideal sine wave shape, and/orcosine wave shape. When the position estimates produced by the firstposition value estimator and/or the second position value estimator aregenerated by an arctan function, as mentioned above, the resultingposition estimate may therefore deviate slightly from the true relativeposition. This deviation, or position error, fluctuates. This deviation,or position error, fluctuates with a period of fluctuation, and that theperiod of fluctuation coincides with the period of the firstpredetermined wavelength of the magneto-electric transducer signals.

The signal treatment module may be adapted to receive a plurality oftrailing transducer head position values and a plurality of leadingtransducer head position values, during the transition period. Thevalues may be collected as signal pairs, each pair including onetrailing transducer head position value and one leading transducer headposition value. The two values in a pair may be collected atsubstantially the same instances.

The signal treatment module may be adapted to calculate an averagedifference value between the trailing transducer head position value andthe leading transducer head position value, average difference valuebeing calculated during the transition period.

The signal treatment module may be adapted to collect at least j signalpairs for the calculation of the average difference value, j being aninteger, e.g., larger than 4, and preferably larger than 7.

The signal treatment module may be adapted to perform a synchronizationprocess during the transition period so as to provide the switching torender a substantially smooth transition from relying on the trailingtransducer head position value to relying on the leading transducer headposition value for the delivery of the encoder output signal.

The deviation value may be used for achieving a smooth transition fromrelying on detector group to relying on detector group.

The encoder may include an encoder user interface adapted to allow auser to select the use of a selectable scale gap indicator signal. Theencoder may allow for the setting of an offset parameter value, which isindicative of a distance from the position of the scale device where theselected scale gap indicator signal is generated to a position of thescale device which may be firmly attached to the shaft. The encoder maybe adapted to identify a reference amplitude value in the signalgenerated by an arctan function generator module. The referenceamplitude value may occur at a position which is located at a distancesubstantially corresponding to the offset parameter value from theposition where the selected scale gap indicator signal is generated, andthe encoder may be adapted to store the reference amplitude value as areference amplitude value.

The selected scale gap indicator signal is generated as described above.

According to example embodiments of the present invention, in a methodfor generating a reference signal by an encoder, e.g., such as thatdescribed above, in which a selected scale gap indicator signal willoccur once per revolution, a distance meter is started in response tothe reception of the selected scale gap indicator signal. When thedistance meter indicates an offset distance from the occurrence of theselected scale gap indicator signal, a comparison is performed between acurrent value of a periodically varying digital signal and the storedreference amplitude value; and, in response to the current valueequaling the stored reference amplitude value, the encoder is adapted togenerate a fix point reference signal.

An encoder output reference signal may be generated in response to thefix point reference signal.

The digital signal may be a signal generated by an encoder as describedabove.

It may be desirable to provide an incremental output signal, in whichthe increments are equally distributed over a revolution without havingto perform any division calculation.

For example, the scale device may have a circumference of 203.64 firstpredetermined divisions Δ₁, i.e. so that the transducers may provide203.64 signal periods on one shaft revolution.

An incremental output signal having 2048 ppr may be provided. This maybe achieved by identifying the nth signal edge by the condition that theposition value >n*step_length, wherestep_length=203.64/(4*2048)=0.02485839844 and n goes from 1 to 8192.

The second last edge of the revolution should come when the positionvalue exceeds the value 8191*step_length=203.6151416.

Unfortunately, it may be slow to calculate that many decimals in an FPGAcircuit.

It may be provided to truncate after four decimals, so that thestep_length=0.0248. The truncated value may lead to an edge positionvalue of 8191*0.0248=203.1368 which may be incorrect even at the firstdecimal.

Another possibility is, for example, to calculate the edge positions by(n*L)/8192for every step so as to avoid the accumulation of truncation errors.

This may be performed easier if the number of pulses per revolution isof the type 2^N, where N is a natural number. However, if the pulse rateis something else, it could take some time to calculate which will delaythe incremental pulse. It may also be difficult to implement a divisionin an FPGA circuit with the large number of bits that is needed in orderto represent a sufficient number of decimals.

The following condition may be used:Position*8192>n*203.64.

The condition according to this arrangement may avoid the truncation andtime delay. In this manner, for example, the 8191st flank is calculatedby the condition:Position*8192>8191*203.64=1.366437888*10^10.

It is a large number so it requires a large number of bits to berepresentable. But that is easy to handle, because no furthercalculation such as a division may be necessary.

An incremental index pulse (Nullimpulse) may be generated in response ton=1.

According to example embodiments, an encoder, for detection ofrotational movement of a rotatable shaft in relation to a part of amachine, includes a scale device for attachment to a circumference ofthe shaft for providing a measuring path. The scale device has a widthand a length and includes a magnetic scale pattern having a plurality ofmagnetic pole elements provided with a first predetermined division inthe direction of the length so as to generate a magnetic field patternat a first distance from a surface of the scale device. A signalgenerator is provided for mounting on the machine part. The signalgenerator includes a housing having a physical extension in a firstdirection parallel to the axis of rotation of the shaft, and a physicalextension in a direction orthogonal to the first direction. The signalgenerator includes a first output terminal for providing an encoderoutput signal indicative of a relative change in position between thesignal generator and the scale device. The signal generator alsoincludes a second output terminal for providing a reference signal, aswell as a first magneto-electric transducer head having a firstmagneto-electric transducer adapted to generate a first electric signalin response to detection of the magnetic field pattern so that the firstelectric signal varies periodically in dependence on the magnetic fieldpattern such that the variation exhibits a first wavelength whichdepends on the first predetermined division when the firstmagneto-electric transducer moves along said magnetic scale pattern. Thesignal generator also includes a first signal processing unit, having afirst device adapted to generate a periodically varying first digitalsignal in dependence on the first electric signal such that thevariation of the first digital signal exhibits the first wavelength whenthe first magneto-electric transducer moves along the magnetic scalepattern, and a device for detecting a signal edge in the periodicallyvarying first digital signal. The signal generator furthermore includesa counter for generating a count value indicative of a number ofdetected signal edges, a memory having a memory location having acertain data value, and an analyzer adapted to generate an indicatorsignal in dependence on a comparison between the count value and thecertain data value, e.g., once per shaft revolution. The signalgenerator also includes an output signal producer adapted to produce theencoder output signal in dependence on the first digital signal, thesecond digital signal, and the scale gap indicator signal. The outputsignal producer is adapted to produce the reference signal in dependenceon the scale gap indicator signal.

Further features and aspects of example embodiments of the presentinvention are described in more detail below with reference to theappended Figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates a perspective view of an encoder systemand parts of a machine to which the encoder system is applied accordingto an example embodiment of the present invention.

FIG. 2 schematically illustrates a block diagram of an encoder systemaccording to an example embodiment of the present invention.

FIG. 3A schematically illustrates a plan view of a portion of a magnetictape according to an example embodiment of the present invention.

FIG. 3B schematically illustrates a perspective view of a portion of amagnetic tape applied to a shaft according to an example embodiment ofthe present invention.

FIG. 3C schematically illustrates a perspective view of a portion of amagnetic tape applied to a shaft according to an example embodiment ofthe present invention.

FIG. 4 schematically illustrates a block diagram of an encoder systemaccording to an example embodiment of the present invention.

FIG. 5 schematically illustrates a block diagram of an encoder systemaccording to an example embodiment of the present invention.

FIG. 6A schematically illustrates signal generation of a magneticencoder according to an example embodiment of the present invention.

FIG. 6B schematically illustrates signal generation of a magneticencoder according to an example embodiment of the present invention.

FIG. 6C schematically illustrates signal generation of a magneticencoder according to an example embodiment of the present invention.

FIG. 6D schematically illustrates signal generation of a magneticencoder according to an example embodiment of the present invention.

FIG. 7A schematically illustrates a perspective view of parts of anencoder system and a measurement object to which the encoder system isapplied according to an example embodiment of the present invention.

FIG. 7B schematically illustrates signal waveforms presented to thesignal processing components of FIG. 2 and/or FIG. 5.

FIG. 7C schematically illustrates a block diagram of a signalinterpreter according to an example embodiment of the present invention.

FIG. 7D schematically illustrates generation of a position estimationsignal according to an example embodiment of the present invention.

FIG. 7E schematically illustrates another perspective view of an encodersystem and parts of a machine to which the encoder system is appliedaccording to an example embodiment of the present invention.

FIG. 8A schematically illustrates a scale device applied having a gapwherein the scale device is applied to a measurement object according toan example embodiment of the present invention.

FIG. 8B schematically illustrates a process of switching between twodetector groups in response to passage of a gap in the scale deviceaccording to an example embodiment of the present invention.

FIG. 8C schematically illustrates a block diagram of an encoder systemaccording to an example embodiment of the present invention.

FIG. 8D schematically illustrates a block diagram of an encoder systemaccording to an example embodiment of the present invention.

FIG. 9A is an illustration showing how gap detection is performed by theencoder system according to an example embodiment of the presentinvention.

FIG. 9B is an illustration showing an implementation of synchronizationassociated to switching between the two detector groups.

FIG. 9C is an illustration showing another implementation ofsynchronization associated to switching between the two detector groups.

FIG. 10A schematically illustrates a cross-sectional view of a scaledevice with a fixpoint or fixpoint region applied to a measurementobject according to an example embodiment of the present invention.

FIG. 10B schematically illustrates a waveform used for generating areference pulse according to an example embodiment of the presentinvention;

FIG. 11 schematically illustrates a flow chart of a method forgenerating a reference pulse using a fixpoint according to an exampleembodiment of the present invention.

DETAILED DESCRIPTION

FIG. 1 is a block diagram illustrating a machine 10 having a rotatableshaft 20. A scale device 30 may be fastened to the shaft 20 so that thescale device 30 moves when the rotatable shaft 20 rotates in relation toa machine part 40. A signal generator 45 may be attachable to themachine part 40. The signal generator 45 may be adapted to generate asignal indicative of a position of the scale device 30 in relation tothe signal generator 45, and/or a signal indicative of a relative changein position between the signal generator 45 and the scale device 30.

The machine 10 may be arranged in a wind power station 10, asillustrated in FIG. 1. Hence, the shaft 20, of the wind power station10, may be attached to one or more turbine/rotor blades 80 adapted tocause rotation of the shaft 20 in response to air movement caused bywind so as to generate electric power by a generator coupled to theshaft 20. The wind power station may be a geared wind power station, adirect drive (gearless) wind power station or a hybrid drive wind powerstation.

The example embodiments described herein may be combined with oneanother. These example embodiments and advantages associated with themare discussed in more detail below.

FIG. 2 is a schematic block diagram illustrating an example embodimentof a system 90 for detecting movement and/or position of a rotatableshaft, such as the shaft 20 of FIG. 1. The encoder system 90 may includea scale device 30 and a signal generator 45. When the encoder system 90is in operation, the signal generator 45 and the scale device 30 aremovable in relation to each other. The signal generator 45 includes adetector device 50 adapted to generate at least one sensor signal inresponse to a relative change in position between the detector device 50and the scale device 30.

The detector device 50 is coupled to a signal processing device 100which is adapted to generate at least one output signal in dependence onthe at least one sensor signal. The at least one output signal isdelivered to an output 110. Hence, the signal generator 45 may beadapted to generate at least one output signal in response to a relativechange in position between the signal generator 45 and the scale device30. The output signal may be a square wave signal or sine signal, asingle-channel or multichannel signal or a signal representing adigitally coded incremental position. Alternatively the output signalmay be signal derived directly from one of these signals or from acombination of these signals.

According to example embodiments, the scale device 30 may include anencoding band 30 which is attachable around the perimeter of the shaft20, the encoding band 30 being providable with information which isdetectable by the detector device 50. Alternatively, the scale device 30may include an encoding ring 30 or an encoding tape 30.

The system 90 may include additional components than the exemplifiedcomponents with reference to FIG. 2. For example the system 90 mayinclude an analog-to-digital (A/D) converter arranged to convert thegenerated at least one sensor signal to a digital representation.Furthermore, the system 90 may include a digital-to-analog (D/A)converter (See FIG. 4) arranged to convert the generated at least oneoutput signal from the signal processing device into an analogrepresentation.

The scale device 30 may include at least one encoding tape such as atleast one magnetic encoding tape, having one or more magnetic scaletracks. The scale device 30 may alternatively include at least onemagnetic encoder ring or encoder belt. The detector device 50 mayinclude a magnetic encoder detector such as a magneto-resistivetransducer (MR), a giant magneto-resistive transducer (GMR), a colossalmagneto-resistive transducer (CMR), a tunneling magneto-resistivetransducer (TMR) or other suitable detector.

FIG. 3A illustrates an example embodiment of a scale device 30 having amagnetic scale pattern 35. The magnetic scale pattern 35 may include aplurality of successive equidistant magnetic pole elements 120.

According to example embodiments, scale device 30 is provided withinformation in the form of a magnetic scale pattern 35. The magneticscale pattern 35 includes a magnetic medium which is provided with agraduation in the form of successive equidistant magnetic pole elements120. Hence, the magnetic scale pattern 35 exhibits incrementalgraduations. The incremental graduations of the scale may include amagnetic pattern having a first predetermined division Δ1, correspondingto the distance between adjacent magnetic pole elements 120, along apath in the direction of arrow Z (See FIG. 3A). When such a scale device30 is used with a magneto resistive sensor unit, the first predetermineddivision Δ1 causes an electric signal having a wave length firstpredetermined wavelength λ1 corresponding to the first predetermineddivision Δ1, as discussed in connection with FIG. 6A.

FIG. 3B is a perspective view of a portion of an example embodiment 30Bof the scale device 30, when applied on the perimeter of a shaft 20. Thescale device 30B has plural equidistant magnetic pole elements, whereinadjacent magnetic pole elements 120 are positioned so that equalmagnetic poles face each other. The magnetic pole elements 120 arepositioned so that the magnetic poles are substantially parallel to thesurface of the shaft 20 onto which the scale device 30B is attached andparallel to the direction of elongation of the scale device 30B, whilethe magnetic pole elements 120 are substantially orthogonal to thedirection of the radius of the shaft 20. The magnetic north of one poleelement faces the magnetic north of the adjacent pole element, asillustrated in FIG. 3B. The magnetic pole elements 120 of the scaledevice 30B may generate magnetic fields having magnetic flux lines thatreach into space at a radial direction from the shaft 20 (see FIG. 1 inconjunction with FIG. 3B) onto which the scale device 30, 30B ismounted.

FIG. 3C is a perspective view of a portion of another example embodiment30C of the scale device 30, shown in FIG. 3A, when applied on theperimeter of a shaft 20. The scale device 30C has plural equidistantmagnetic pole elements 120, wherein all magnetic pole elements 120 arepositioned so that the magnetic poles are directed in a substantiallyradial direction in relation to the shaft 20. The magnetic pole elements120 are positioned so that every other magnetic pole element 120 has amagnetic pole directed in the radial direction out from the center ofthe shaft 20, and the remaining magnetic pole elements have a magneticpole directed in the radial direction in towards the center of the shaft20, as shown in FIG. 3C.

Whereas both of the scale devices 30B and 30C generate a magnetic fieldthat can be used as an incremental encoder scale, the example embodimentillustrated in FIG. 3C may allow cutting the band to a desired lengthwhile avoiding the creation of a magnetic pole having a shorter polelength λ.

FIG. 4 is a block diagram illustrating an example embodiment 90B of theencoder 90 for detecting movement and/or position of a rotatable shaft,such as the shaft 20 of FIG. 1.

With reference to FIG. 4, the encoder 90 may include a scale device 30,and a signal generator 45. When the encoder system 90 is in operation,the signal generator 45 and the scale device 30 are movable in relationto each other, as discussed in connection with FIGS. 1 and 2 above. Thesignal generator 45 includes a first detector group 50:1 and a seconddetector group 50:2. The first detector group 50:1 includes a firsttransducer 50:1A adapted to generate a first electric signal A1, and asecond transducer 50:1B adapted to generate a second electric signal B1.The first electric signal A1 and the second electric signal B1constitute a first signal pair A1B1.

The first transducer 50:1A may be coupled to deliver the analog firstelectric signal A1 to a first A/D converter 125:1A which may be adaptedgenerate a digital signal A1 _(D) in response to the analog firstelectric signal A1. Similarly, the second transducer 50:1B may becoupled to deliver the analog second electric signal B1 to a second A/Dconverter 125:1B which may be adapted generate a digital signal B1 _(D)in response to the analog second electric signal B1.

The second group 50:2 of detector elements may include a thirdtransducer 50:2A adapted to generate a third electric signal A2, and afourth transducer 50:2B adapted to generate a fourth electric signal B2.

The third transducer 50:2A may be coupled to deliver the analog thirdelectric signal A2 to a third A/D converter 125:2A which may be adaptedgenerate a digital signal A2 _(D) in response to the analog thirdelectric signal A2. Similarly, the fourth transducer 50:2B may becoupled to deliver the analog fourth electric signal B2 to a fourth A/Dconverter 125:2B which may be adapted generate a digital signal B2 _(D)in response to the analog second electric signal B2.

Each of the A/D converters 125:1A 125:1B 125:2A 125:2B sample theirrespective signals A1, B1, A2, and B2, respectively, at a predeterminedsample rate f_(S).

The signal generator 45 may also include a data processing unit 100capable of controlling the operation of signal generator 45 inaccordance with program code. The data processing unit 100 may also becoupled to a memory 102 for storing said program code. According toexample embodiments, the data processing unit 100 may be adapted toreceive the digital signals A1 _(D) B1 _(D), A2 _(D) and B2 _(D).

The program memory 102 may include a non-volatile memory. The memory 102may be a read/write memory, i.e., providing both reading data from thememory and writing new data onto the memory 102. According to exampleembodiments, the program memory 102 includes a FLASH memory. Accordingto example embodiments, the program memory 102 is integrated in the dataprocessing unit 100 so that the program functions to be executed by thedata processing unit 100 are stored within the data processing unit 100itself.

The data processing unit 100 may also be coupled to a read/write memory104 for data storage. According to example embodiments, the read/writememory 104 includes a non-volatile memory. This means that data writteninto the non-volatile read/write memory 104 will be retained even whenthe memory 104 is not powered.

When, in the following, it is described that the data processing unit100 performs a certain function this is to be understood that, e.g., thedata processing unit 100 performs a certain part of the program which isstored in the memory 102.

The data processing unit 100 may also be coupled to a user interface 170via a data bus 180. The user interface 180 may include a display 182and/or data input device 184, such as buttons 184 and or a touch screen182/184 adapted to allow a user to feed data into the encoder via thedisplay 182 on which the encoder supplies user information output.

A user of the encoder 90 may be provided with information messages bycharacters being displayed on the display 182. A particular message maybe displayed in response to a certain event.

The data processing unit 100 may be coupled to the memory 102 by a databus, and to the read/write memory 104 by another data bus. The dataprocessing unit 100 may also communicate with a data port 200 by a databus 210.

The wording “a computer program product, loadable into a digital memoryof an encoder” means, for example, that a computer program can beintroduced into a digital memory of an encoder 90, such as, e.g., thememory 102, so as to obtain an encoder programmed to be capable of, oradapted to, carrying out a method of the kind described herein. The term“loaded into a digital memory of a condition analysing apparatus” means,for example, that an encoder programmed in this manner is capable of, oradapted to, carrying out a method of the kind described herein.

The above mentioned computer program product may also be loadable onto acomputer readable medium, such as a compact disc or DVD or USB memorystick. Such a computer readable medium may be used for delivery of theprogram to a client, in that the program may be loaded from the computerreadable medium to the program memory 102, e.g., via port 200.

The data processing unit 100 may include a central processing unit, ormicroprocessor, for controlling the operation of the encoder 90.Alternatively, the data processing unit 100 may include a Digital SignalProcessor (DSP).

According to example embodiments, the data processing unit 100 includesa Field Programmable Gate Array circuit 100, also referred to as anFPGA. The Field Programmable Gate Array circuit 100 may provide acombination of flexibility and very high performance to the encoder 90in that a large amount of data can be processed relatively fast by theField Programmable Gate Array circuit. This arrangement may provide forsimultaneous signal treatment of two, three, or four detector signals,such as the digital signals A1 _(D), B1 _(D), A2 _(D), and B2 _(D).Moreover, the functions executed by the FPGA may be software controlledand the FPGA allows for truly parallel processing, which alsocontributes to increased performance to the encoder 90. Hence, the FPGA100 may be coupled to receive, in real time, the digital signals A1_(D), B1 _(D), A2 _(D), and B2 _(D) all of which are digital signalshaving a sample rate f_(S).

The data processing unit 100 may be arranged to execute the program codestored in the memory 102 so as to cause the encoder 90 to execute one orseveral programs so as to cause any of the processes described herein tobe executed.

FIG. 5 is a block diagram illustrating an example embodiment of thesystem 90, 90B for detecting movement and/or position of a rotatableshaft, such as the shaft 20 of FIG. 1.

The system 90 may include a scale device 30 attached to a shaft 20 of amachine 10, as discussed in connection with FIGS. 1 to 4 above.

The system 90C may also include a detector device 50 having a firstdetector group 50:1 and a second detector group 50:2. The first detectorgroup 50:1 may include a first transducer 50:1A and a first A/Dconverter 125:1A adapted generate a digital signal A1 _(D), and a secondtransducer 50:1B and a second A/D converter 125:1B adapted generate adigital signal B1 _(D) as described above in connection with FIG. 4.

Similarly, the second detector group 50:2 may include a third transducer50:2A coupled to a third A/D converter 125:2A which may be adaptedgenerate a digital signal A2 _(D) in response to the analog secondelectric signal B1, and a fourth transducer 50:2B and a fourth A/Dconverter 125:2B which may be adapted generate a digital signal B2 _(D)as described above in connection with FIG. 4.

Each of the A/D converters 125:1A 125:1B 125:2A 125:2B sample theirrespective signals A1, B1, A2, and B2, respectively, at a predeterminedsample rate f_(S) so as to generate corresponding digital signals A1_(D), B1 _(D), A2 _(D), and B2 _(D), respectively.

The digital signals are delivered to the data processing unit 100. Thedata processing unit 100, when executing the programs stored in thememory 102, as described above in connection with FIG. 4, will performfunctions which are described with reference to the block diagram ofFIG. 5. Hence, according to example embodiments, the blocks denoted byreference numerals 150:1, 150:2, 220, 230 represent functions that maybe performed by the data processing unit 100. As mentioned above, thedata processing unit 100 may include a Field Programmable Gate Arraycircuit 100.

With reference to FIG. 1 and FIG. 5, it should be understood that whenthe shaft 20 rotates, the magnetic scale device 30 will move in relationto the detector unit 50.

With reference to FIG. 5, the encoder 90,90B may include a firstposition value estimator 150:1 for generating a first position valueestimate Z_(EST1) in dependence on at least one of the digital signalsA1 _(D) and B1 _(D).

The system 90, 90B may also include a second position value estimator150:2 for generating a second position value estimate Z_(EST2) independence on at least one of the digital signals A2 _(D) and B2 _(D).

According to example embodiments, the first position value estimator150:1 includes a first signal pair interpreter 150:1 adapted to receivethe digital signals A1 _(D) and B1 _(D). The first signal pairinterpreter 150:1 is adapted to generate a first estimated positionsignal Z_(est1) in dependence on the received signal pair.

The system 90, 90B may also include a second signal pair interpreter150:2 adapted to receive the second signal pair A2 _(D), and B2 _(D).The second signal interpreter 150:2 is adapted to generate a secondestimated position signal Z_(est2) in dependence on the received signalpair A2B2. This will be described in more detail in connection with,e.g., FIG. 7C.

Correlation between scale division and transducer output wavelength isdescribed below.

FIG. 6A is an illustration showing the transducer 50:1A of FIG. 5, and ascale device 30 having a magnetic scale pattern 35, as discussed inconnection with FIGS. 3A, 3B, and/or 3C.

FIG. 6A illustrates a transducer 50:1A moving, in relation to the scaledevice 30, along a measuring path Z in the direction of the arrow (whichis also denoted Z) at a distance D_(S) from the surface of the scaledevice 30. Hence, the direction of travel of the transducer 50:1A isfrom the left to the right in FIG. 6A.

As shown in FIG. 6A, the magnetic pole elements 120 generate magneticfields forming a magnetic field pattern 240 corresponding to themagnetic scale pattern 35. The magnetic field pattern 240 may bedetectable at a distance D_(S) from the surface of the scale device 30.The magnetic fields are illustrated by magnetic flux lines 250 in FIG.6A.

The magneto-resistive transducer output wavelength is described below.

According to example embodiments, the transducer 50:1A includes amagneto-resistive transducer, whose resistance depends on the directionof the magnetic field passing through the magneto-resistive transducerbody. When the magneto-resistive transducer moves along the measuringpath z (in the direction of the arrow z as illustrated in FIG. 6A), theresistance of the magneto-resistive transducer will vary in dependenceof the magnetic field pattern 240, and an amplitude of a detectionsignal may vary as illustrated by the diagram 160 in the upper portionof FIG. 6A. Hence, when the transducer 50:1A is supplied with apredetermined voltage, the current flowing through the transducer 50:1Awill also vary, as illustrated by the diagram 160 in the upper portionof FIG. 6A, in dependence of a relative change in position between thesignal generator 45 and the scale device 30.

According to example embodiments, the magneto-resistive transducer 50:1Amay be connected in a bridge circuit, such as a Wheatstone bridge or aCarey Foster bridge. This may improve the accuracy with which theresistance variation of the magneto-resistive transducer may bedetected.

As discussed in connection with FIGS. 3A and 3B, the incrementalgraduations of the scale may include a magnetic pattern having a firstpredetermined division Δ1, corresponding to the distance betweenadjacent magnetic pole elements 120, along a path in the direction ofarrow Z (See FIG. 3A and/or FIG. 6A). When such a scale device 30 isused with a magneto-resistive sensor unit, the first predetermineddivision Δ1 may cause an electric signal A1 having an amplitude to varywith a first predetermined wavelength λ1 corresponding to the firstpredetermined division Δ1, as illustrated in FIG. 6A. Hence, when themagneto-resistive sensor unit moves the first predetermined distance Δ₁along the measuring path z, the analog electric signal A1 will exhibitone first predetermined wavelength λ1.

Hence, when the incremental graduations of the scale includes a magneticpattern having a first predetermined division Δ1, a magneto-resistivetransducer 50:1A, when moving along the measuring path Z, may generatean oscillating signal A1 in response to a detected magnetic fieldpattern 240. The oscillating analog electric transducer signal A1 maydepend on transducer movement along the scale direction Z so as toexhibit one first predetermined wavelength λ1 in response to moving onedivision Δ1.

The Hall transducer output wavelength is further described below.

According to example embodiments of the encoder 90, 90B, the transducer50:1A may be a Hall transducer. FIG. 6B is an illustration of thecorrelation between magnetic scale pattern 35 and the transducer outputsignal wave length in the case that the transducer 50:1A is a Halltransducer.

The Hall transducer may include an indium compound semiconductor crystalsuch as indium antimonide. When the Hall transducer is positioned sothat the magnetic field lines are passing at right angles through theHall transducer, the transducer may provide an output indicative of thevalue of magnetic flux density.

A current is passed through the crystal of the Hall transducer which,when placed in a magnetic field has a voltage occurring across it due tothe “Hall effect”. The Hall effect occurs due to a conductor beingpassed through a uniform magnetic field. When the Hall transducer movesalong the measuring path in the direction z, the output of the Halltransducer will vary, as illustrated by the diagram 160 in the upperportion of FIG. 6B.

As discussed in connection with FIGS. 3A and 3B, the incrementalgraduations of the scale may include a magnetic pattern having a firstpredetermined division Δ1, corresponding to the distance betweenadjacent magnetic pole elements 120, along a path in the direction ofarrow Z (See FIG. 3A and/or FIG. 6A). When such a scale device 30 isused with a Hall transducer unit, the first predetermined wavelength λ1of the electric output signal from the Hall transducer unit correspondsto 2*Δ₁, as illustrated in FIG. 6B. Hence, when the Hall transducer unitmoves a distance of twice the first predetermined distance Δ1 along themeasuring path z, the analog electric signal A1 will exhibit one firstpredetermined wavelength λ1.

FIG. 6C is an illustration of the correlation between magnetic scalepattern 35 and the wave length and phase of the transducer outputsignals wave length when the transducers 50:1A and 50:1B aremagneto-resistive transducers.

According to example embodiments, the first lagged magneto-electrictransducer (50:1B), having a direction of sensitivity, is positioned ata geometrical distance from the first magneto-electric transducer(50:1A), also having a direction of sensitivity. The firstmagneto-electric transducer (50:1A) and the first laggedmagneto-electric transducer (50:1B) are arranged such that theirrespective directions of sensitivity are substantially parallel. Thefirst lag (PD) depends on the geometrical distance. According to exampleembodiments, the geometrical distance between the two transducers is aquarter of the first predetermined division (Δ₁). This arrangementrenders the first lag (PD) to become a quarter wavelength. However, if adifferent scale device is used, having a different predetermineddivision Δ₃, deviating from the first predetermined division Δ₁ then theelectrical signals A1 and B1 will have another phase relationship.

According to example embodiments, the first lagged magneto-electrictransducer (50:1B), having a direction of sensitivity, is positioned ingeometrical proximity to the first magneto-electric transducer (50:1A),also having a direction of sensitivity. The first magneto-electrictransducer (50:1A) and the first lagged magneto-electric transducer(50:1B) are arranged such that there is a geometrical angle betweentheir respective directions of sensitivity, and the first lag (PD)depends on the geometrical angle.

This arrangement renders the first lag (PD) to be independent of thefirst predetermined division (Δ₁) of the scale device. Hence, the firstmagneto-electric transducer head (50:1) having the firstmagneto-electric transducer (50:1A) and the first laggedmagneto-electric transducer (50:1B) may be used together with differentscale devices 30 having mutually different first predetermined divisions(Δ₁). Likewise, the second magneto-electric transducer head (50:2),having the second magneto-electric transducer (50:2A) and the secondlagged magneto-electric transducer (50:2B), may be made in the samemanner as described for the first magneto-electric transducer head(50:1). In this manner, a flexible signal generator (45, 50) may beachieved, thus rendering usability with various magnetic scale deviceshaving mutually different first predetermined divisions (Δ₁).

According to example embodiments, the geometrical angle is substantially45 degrees, as illustrated in FIG. 6C. This arrangement renders thefirst lag (PD) of the magneto-electric transducer head to become aquarter wavelengths irrespective of the first predetermined division(Δ₁) distance.

According to example embodiments, the geometrical proximity is such thatthe first magneto-electric transducer (50:1A) and the first laggedmagneto-electric transducer (50:1B) are arranged at substantially thesame location, such as, for example, with substantially no distancebetween the first lagged magneto-electric transducer (50:1B) and thefirst magneto-electric transducer (50:1A).

FIG. 6D is an illustration of the correlation between magnetic scalepattern 35 and the transducer output signals wave length in the casethat the transducers 50:1A and 50:1B are Hall transducers.

With reference to FIG. 6D, the first lagged magneto-electric transducer(50:1B) and the first magneto-electric transducer (50:1A) may be Hallsensor transducers. One first wavelength (λ₁, λ_(1MR), λ_(1H)) may thenbe generated by relative movement along the distance of the two firstpredetermined divisions (Δ₁). According to example embodiments, thefirst lagged magneto-electric transducer (50:1B), having a direction ofsensitivity, is positioned in geometrical proximity to the firstmagneto-electric transducer (50:1A), also having a direction ofsensitivity, in which the first magneto-electric transducer (50:1A) andthe first lagged magneto-electric transducer (50:1B) are arranged suchthat there is a geometrical angle between their respective directions ofsensitivity. The first lag (PD) depends on the geometrical angle.

According to example embodiments, the geometrical angle is substantiallyninety degrees. This renders the first lag (PD) of the magneto-electrictransducer head to become a quarter wavelength irrespective of the firstpredetermined division (Δ₁) distance, when Hall sensor transducers areused.

FIG. 7A is an illustration showing an exemplary configuration of partsof an encoder system applied to a measurement object 20, such as arotating shaft rotating axially in a direction Z.

As shown in FIG. 7A, a scale device 30, e.g., in the form of a magneticencoding tape, may be applied circumferentially around the measurementobject 20. The scale device 30 may be as described above, e.g., inconnection with FIGS. 3A, 3B, and/or 3C. Hence, the scale device 30includes a number of magnetic north and south poles, the magnetic northand south poles of the magnetic scale device being arranged in analternating fashion in a circumferential direction. The magnetic northand south poles are further arranged at equidistant intervals of apredetermined distance, e.g., the first predetermined division Δ₁. Afirst detector group 50:1 and a second detector group 50:2 may bearranged so that each of the two detector groups 50:1 and 50:2 arepositioned above and substantially parallel to the scale device 30. Thefirst and second detector groups 50:1, 50:2 may be arranged to sense themagnetic fields generated by the magnetic poles of the scale device asdiscussed with reference to FIG. 6A.

Each magnetic pole forms an increment so that when passed by a detectorgroup (one of first detector group 50:1 and second detector group 50:2),a pulse can be generated, in which the incremental pulse indicatesincremental shaft rotation, i.e., incremental rotation of themeasurement object, as discussed in connection with FIGS. 6A and 6B.

In the illustrated example, with reference to FIG. 7A, the number ofpoles also referred to as pole number PN is 32. This means that PNincrements may be generated for each revolution of the rotating shaft,when a magneto-resistive transducer is used. Hence, when PN=32, therewill be 32 increments generated for each revolution of the rotatingshaft when a magneto-resistive transducer is used. In case a Halltransducer is used, the number of increments would be PN/2 for eachrevolution of the rotating shaft. Hence, when PN=32, there will be 16increments generated for each revolution of the rotating shaft when aHall transducer is used.

It should be noted that the number of poles may be different compared tothe illustrated example with reference to FIG. 7A. For example, fewer ormore poles could be implemented by forming more or fewer magneticalternating magnetic poles in the scale device. As an example, thenumber of poles could instead be in the range of 2 to 100,000, such asfor example 1,024 or 2,048. The number of poles actually used in a scaledevice 30 may depend on application, shaft diameter and desiredresolution to be achieved in the encoder output signal.

FIG. 7B is an illustration showing a signal generation resulting fromdetector groups 50:1, 50:2 passing over a moving scale device, such asthat exemplified with reference to FIG. 7A.

As shown in FIG. 7B, waveforms in the form of sine and cosine signalsare generated resulting from each of the detector groups passing over ascale device moving in a direction Z, such as illustrated with referenceto FIG. 7A.

According to example embodiments, each of the first detector group 50:1and second detector group 50:2 includes two magneto-resistivetransducers. The first detector group may include a first transducer50:1A adapted to generate a first electric signal A1 so that itoscillates in dependence on movement in the direction Z at a distancefrom the scale device 30, and a second transducer 50:1B may be adaptedto generate a second electric signal B1 so that it oscillates independence on movement in the direction Z at a distance from the scaledevice 30. Examples of the waveforms of signals A1 and B1 are visible inthe upper portion of FIG. 7B. The second transducer 50:1B is adapted togenerate the second electric signal B1 at a lag in relation to the firstelectric signal A1. In other words, the first and second electricsignals are generated such that there is a phase deviation PD betweenthe first electric signal A1 and the second electric signal B1. The signof the phase deviation PD may be indicative of the direction of movementof shaft 20.

The second detector group may include a third transducer 50:2A adaptedto generate a third electric signal A2, and a fourth transducer 50:2Badapted to generate a fourth electric signal B2. Examples of thewaveforms of signals A2 and B2 are illustrated in the lower portion ofFIG. 7B.

As mentioned above, the first transducer and the second transducer ofthe first detector group are mutually configured so that there is aphase lag PD between the signals A1 and B1. According to exampleembodiments, the first electric signal A1 may substantially form a sinewave and the second electric signal B1 may substantially form a cosinesignal. Hence, according to example embodiments:A1=sin(z), andB1=cos(z),

in which z represents the distance along the measuring path.

Hence, according to this example embodiment, the second electric signalB1 may be 90 degrees out of phase from the first electric signal A1.With reference to FIG. 7A in conjunction with FIG. 7B, it should beunderstood that when shaft 20 rotates clockwise (i.e., in the directionof the arrow Z) the phase deviation between signals A1 and B1 may be +90degrees, and conversely, when the shaft 20 rotates counterclockwise(i.e., in the opposite direction of the arrow Z) the phase deviationbetween signals A1 and B1 may be −90 degrees. Hence, the sign (+ or −)of the phase deviation between signals A1 and B1 may be used fordetermining the direction of rotation of the shaft 20.

Accordingly, the second electric signal B1 may be a quadrature signal ofthe first electric signal A1. This may, for example, be achieved byconfiguring relative positioning or angular displacement between thefirst and second transducer of the first detector group.

In a similar fashion, the third signal A2 of the third transducer of thesecond detector group may substantially form a sine signal, and thefourth electric signal of the fourth transducer of the second detectorgroup may substantially form a cosine signal. Hence, the fourth electricsignal B2 may substantially be the quadrature signal of the thirdelectric signal A2. This means that the phase difference PD both betweenthe first and second electric signal and between the third and fourthelectric signal is 90 degrees. Hence, according to an exampleembodiment:A2=sin(z), andB2=cos(z),

in which z represents the distance along the measuring path.

Accordingly, the sign (+ or −) of the phase deviation between signals A2and B2 may also be used for determining the direction of rotation of theshaft 20.

FIG. 7C is an illustration showing a block diagram of the first signalinterpreter 150:1.

With reference to FIG. 5 and as shown in FIG. 7C, the signals A1 _(D)and B1 _(D) in the form of a sine and a cosine signal from the firstdetector group 50:1, such as exemplified in FIG. 7A, 7B, are fed intothe signal interpreter 150:1 associated to the first detector group.

According to example embodiments, the signal interpreter 150:1 includesan arctan function generator module 260:1 arranged to process the A1_(D) and B1 _(D) signals by performing an arctan calculation function.The output value S_(EA) generated by the arctan function generatormodule 260:1 may represent an electrical angle (EA), i.e., a valueprogressing from zero to 2Π in dependence on signals A1 _(D) and B1_(D). Hence, with reference to FIG. 6A or 6B in conjunction with FIG.7B, the output signal S_(EA1) from indicates the relative position ofthe transducer 50:1A signal within one wave length λ1.

The signal interpreter further includes a rotational direction detectormodule 270:1, RDM arranged to detect the rotational direction of thescale device. The rotational direction detector module 270:1 may bearranged to detect the current direction of rotation (clockwise,counterclockwise) in dependence on a detected phase relation between theA1 and B1 signal. According to example embodiments, when the secondelectric signal B1 _(D) is a quadrature signal of the first electricsignal A1 _(D), the rotational direction detector module 270:1 may bearranged to detect the sign (+ or −) of the phase deviation betweensignals A1 _(D) and B1 _(D), so as to generate an output signal RD1which may be indicative of the rotational direction of the shaft 20.

According to example embodiments, the rotational direction detectormodule 270:1 includes a phase deviation analyzer 272:1 having inputs forreceiving the signals A1 _(D) and B1 _(D). The phase deviation analyzer272:1 may be adapted to establish a value PD_(EST1) indicative of thecurrent phase deviation between signals A1 _(D) and B1 _(D). Theanalyzer may also have an input for receiving at least two valuesindicative of “Normal” phase deviation PD_(NORM). When the signals A1_(D) and B1 _(D), are quadrature signals, the “Normal” phase deviationPD_(NORM) values may be, e.g., +90 degrees and −90 degrees,respectively, each value corresponding to one of the two rotationaldirections of shaft 20.

The phase deviation analyzer 272:1 may be adapted to compare theestablished value PD_(EST1) with the two values indicative of “Normal”phase deviation PD_(NORM). When the comparison indicates that theestablished value PD_(EST1) substantially corresponds to one of the twovalues indicative of “Normal” phase deviation PD_(NORM), this ininterpreted to indicate that the corresponding detector head 50:1 ispositioned above the scale pattern 35.

When the comparison, performed by phase deviation analyzer 272:1,indicates that the established value PD_(EST1) deviates from both of thetwo values indicative of a “Normal” phase deviation PD_(NORM) the phasedeviation analyzer 272:1 may be adapted to generate a phase error signalPDE1. This signal may be used for detecting a scale edge, as discussedin connection with FIG. 8B below.

An example embodiment of scale edge detection is described below.

With reference to FIG. 7C, the phase error signal PDE1, generated by thephase deviation analyzer 272:1, may be used an indication to the effectthat the detector head 50:1 is positioned above the scale pattern 35.Hence, the position Z at which the phase error signal PDE1 occurs mayindicate that the detector head 50:1 is passing a scale edge at thatposition. Hence the occurrence of the phase error signal PDE1 mayindicate that detector head 50:1 is just entering a gap in the scale atthat position Z. Hence, the phase error signal PDE1 switching from “Nophase error” to “Phase error indication” may indicate that detector head50:1 is just entering a gap in the scale at that position Z.

When that occurs, the encoder may be adapted to store that positionvalue Z, i.e., the position value Z generated by 220, as a scale endedge position value ZSE:1 for detector head 50:1.

Similarly, when the phase error signal PDE1 switches from “Phase errorindication” to “No phase error” this may indicate a position Z at whichthe detector head 50:1 has just passed scale start edge, i.e., thedetector head 50:1 is just beginning to read the magnetic field pattern240 caused by the scale pattern 35. Thus, when the phase error signalPDE1 switches from “Phase error indication” to “No phase error” this mayindicate that detector head 50:1 has just left the gap 340 and enteredthe region of the scale pattern 35.

The signal interpreter 150:1 further includes a counter module 280:1which may be arranged to count the number of rising or falling edgesappearing on the signal SEA:1 delivered by the arctan function generator260:1. The resulting count value PN of counted rising or falling edgesmay be indicative of the number poles of the scale device the firstdetector group has passed, since the last reset of the counter module280:1. Hence, the output signal PN delivered by counter module 280:1 maydeliver the value PN, as discussed above in relation to FIG. 7A.

The counter module 280:1 may further be arranged to receive informationrelating to rotational direction from the rotational direction module270:1 so as to allow the counter module 280:1 to handle both rotationaldirection that is clockwise and counter clockwise, e.g., by increasingthe counter value PN in response to clockwise rotation of the shaft 20and decreasing the counter value PN in response to counterclockwiserotation of the shaft 20 (See FIG. 7C in conjunction with FIG. 7A andFIG. 1).

The signal interpreter 150:1 further includes a memory portion 285,which may be referred to as a wavelength storage module λM. Thewavelength storage module may be arranged to store a parameter Dcorresponding to the physical wavelength of a magnetic pole element.With reference to the discussion in connection with FIGS. 6A, 6B and 3C,the wavelength storage module λM may adapted to deliver information Dindicative of the relation between the first predetermined division Δ₁and the first predetermined wavelength λ₁. According to an embodiment,the information D may have the dimension mm/(degree of electrical angleEA).

The wavelength storage module λM may be connected to a fractionaldistance value module 290, which may be arranged to process the valueS_(EA) delivered by the arctan function generator module 260:1 and theparameter D provided by the wavelength storage module.

The fractional distance value module 290 may be arranged to multiply theparameter D with the latest received value SEA:1, delivered by thearctan function generator 260:1, so that a fractional lambda valueλ_(F1) is generated, in which the fractional lambda value λ_(F1) mayrepresent the current physical distance within one wavelength. Hence,for example, if MR transducers are used, we may refer to FIG. 6A: If thefirst predetermined division Δ₁ is 5 mm, and the current value S_(EA1)=Πor 180 degrees, then the value D will be 5 mm/λ1, and the fractionallambda value λ_(F1) delivered by the fractional distance value module290 may represent 2.5 mm, i.e., half of the physical distance Δ₁.

The signal interpreter 150:1 may further include a position estimationmodule 300 arranged to produce a first estimate Z_(EST1) of the currentposition of the scale device 30 in relation to the detector device 50(See FIG. 1 in conjunction with FIG. 7A and FIG. 7C). The positionestimation module 300 may be arranged to generate the first estimateZ_(EST1) of the current position in dependence on the fractional lambdavalue λ_(F1) from fractional distance value module 290 and the countvalue PN received from the counter module 280:1.

With reference to FIG. 5 and FIG. 7C, the second signal interpreter150:2 may operate in the same manner as described for the first signalinterpreter 150:1.

Hence, the second signal interpreter 150:2 may include a positionestimation module 300:2 arranged to produce a second estimate Z_(EST2)of the current position of the scale device 30 in relation to thedetector device 50 in dependence on the A2 _(D) and B2 _(D) signals (SeeFIG. 5 in conjunction with FIGS. 1, 7A and FIG. 7C).

The second signal interpreter 150:2 may also include a rotationaldirection detector module 270:2 which may be arranged to detect thecurrent direction of rotation (clockwise, counterclockwise) independence on a detected phase relation between the A2 and B2 signal.According to example embodiments, when the electric signal B2 _(D) is aquadrature signal of the electric signal A2 _(D), the rotationaldirection detector module 270:2 may be arranged to detect the sign (+ or−) of the phase deviation between signals A2 _(D) and B2 _(D), so as togenerate an output signal RD2 which may be indicative of the rotationaldirection of the shaft 20.

Moreover, the second signal interpreter 150:2 may also include a phasedeviation analyzer 272:2 corresponding to the phase deviation analyzer272:1 as described above.

FIG. 7D is an illustration showing processing of signals, generatedresulting from the one of the detector groups passing over a movingscale device such as described with reference to FIG. 7A.

As shown in the upper portion of FIG. 7D, a waveform acrtanf1 isgenerated by processing the electric signals A1 and B1 generated by thefirst detector group, as described with reference to FIG. 7B. Theprocessing may be performed by the processing device 100, as illustratedwith reference to FIG. 2 and/or FIGS. 4 and 5.

According to example embodiments, the first A1 and second B1 electricsignals generated by the first detector group 50:1 are processed byusing an arctan according to equation 1 below.

$\tan^{- 1}\left( \frac{A\; 1}{B\; 1} \right)$

By processing the arctan function as described above, an electricalangle value EA, S_(EA) can be derived. Hence, a current value of thevariable S_(EA) is indicative of the position within each pole. Theelectrical angle value S_(EA) starts from 0 and progresses to 2π foreach pole or λ, as discussed above.

As shown in the lower portion of FIG. 7D, a modified waveform αA isprovided by processing the waveform arctanf1. The waveform αA isindicative of the mechanical angle, e.g., estimated position Z_(EST1) EPof the measurement object, such as the incremental rotation of the shaft20 illustrated with reference to FIG. 7A. The progression of pole numberPN is indicated to the right in the lower portion of FIG. 7D and theestimated position is indicated to the left in the lower portion of FIG.7D.

The waveforms or third and fourth electric signals A2, B2 may beprocessed in a similar fashion to the first and second electric signalsas explained above in order to derive an electrical angle and amechanical angle.

FIG. 7E is a block diagram illustrating another machine 10, as comparedto the machine illustrated in FIG. 1. Certain machines 10, having ashaft 20, may have a shaft portion 310 which is positioned such that itis difficult or even impossible to place anything around that shaftportion 310 from an end of the shaft 20. In other words, theconfiguration of the machine 10 may be such that threading a unitarycircular scale device 30 (See FIG. 7A in conjunction with FIG. 7E andFIG. 1) into a desired position may be prevented by a machine part. Withreference to FIG. 7E, the length of the shaft 20 may stretch from theone machine part 40 to another machine part 320, in which the first andsecond machine parts 40, 320 are shaped and dimensioned so thatthreading, e.g., a band, shaped as a single-piece closed circle, overthe first or second machine parts 40, 320 is impossible. Hence, when itis desired to measure and detect the position and/or rotational movementof the shaft 20, it may not be possible to attach a single-piececircular magnetic scale at the shaft portion 310. Additionally, theamount of space, in the direction of the axis of rotation 330 of theshaft 20, may be limited. Hence the physical reality of the machine mayrequire the width of the scale device 30 to be small.

The machine 10 may be arranged as a wind power station 10, asillustrated in FIGS. 1 and 7E. Hence, the shaft 20, of the wind powerstation 10, may be attached to one or more turbine/rotor blades 80adapted to cause rotation of the shaft 20 in response to air movementcaused by wind so as to generate electric power by a generator 70coupled to the shaft 20. In connection with maintenance work on somemachines, such as wind power station 10, it may be necessary to obtainnot only information about relative position, but information about anabsolute position of the shaft 20. For instance, it may be necessary tostop the wind power station from operation by introducing a lock bolt,or similar into a corresponding bolt receptor in the shaft so as to lockthe shaft in a certain position. In order to be able to introduce thelock bolt, it may be necessary to position the shaft so that the boltreceptor faces the position of the lock bolt.

Hence, there is a need to achieve an encoder 90 capable of delivering anabsolute position, while also being capable of being mounted so that itrequires a very limited amount of space. Moreover, it may be needed tomake it possible to install the encoder 90, even when first and secondmachine parts 40, 320 are shaped and dimensioned so that threading,e.g., a band, shaped as a single-piece closed circle, over the first orsecond machine parts 40, 320 is impossible.

According to example embodiments, the scale device 30 may be dividableso as to allow it to be placed at shaft positions such as shaft portion310. According to example embodiments, the scale device 30 may then alsobe provided with a gap portion 340.

According to example embodiments, the scale device 30 may be made of aflexible band, such as, e.g., a bendable steel band, provided with anopenable locking device so as to allow the flexible band to be openedsuch that it may be placed at a desired measuring path position on theshaft 20. When positioned at the desired measuring path position on theshaft 20, the locking device of the flexible scale band 30 may be closedand locked so as to attach it to the desired measuring path position onthe shaft 20. The locking device may then be used as the gap portion 340of the scale device 30.

According to example embodiments, the scale device 30 may include adividable scale ring. The inner diameter of the dividable ring maysubstantially correspond to the outer diameter of a shaft 20 to whichthe dividable scale ring 30 is intended to be attached. The dividablescale ring 30 may then have at least two openings so as to allow thering to be divided in at least two parts. Hence, an opening of thedividable scale ring 30 may be provided with an openable locking deviceso as to allow the dividable scale ring 30 to be opened such that it maybe placed at a desired measuring path position on the shaft 20. Whenpositioned at the desired measuring path position on the shaft 20, thelocking device of the dividable scale ring 30 may be closed and lockedso as to attach it to the desired measuring path position on the shaft20. The locking device may then be used as the gap portion 340 of thescale device 30.

FIG. 8A illustrates a magnetic scale device 30 when attached around theperimeter of a shaft 20. As illustrated by FIG. 8A, the magnetic scaledevice 30 includes at least one gap 340 in the magnetic scale pattern35, when the magnetic scale device 30 is attached around the perimeterof a shaft 20. Hence, whereas the magnetic scale pattern 35 displays aplurality of successive equidistant magnetic pole elements 120, thescale gap portion 340 of the scale device 30 may lack magnetic poleelements. Alternatively, the scale gap portion 340 of the scale device30 may be arranged so as to exhibit a second predetermined wavelength λ₂differing from the first predetermined wavelength λ₁. This may beachieved by providing pole elements with a second predetermined divisionΔ₂ differing from the first predetermined division Δ₁.

The magnetic scale device 30, as illustrated in FIG. 8A, may include asingle magnetic scale pattern 35 forming a single magnetic track alongthe measuring path Z circumscribing the shaft 20.

Detector switch resulting from gap passage is described below.

FIG. 8B is an illustration showing a gap passage with associatedswitching of output signals from detector groups.

As shown in FIG. 8B, the first and second detector groups 50:1, 50:2pass a gap 340 formed between two portions 30:1, 30:2 of a scale deviceas a result of a measurement object to which the scale device isattached travels in a direction Z. The detector groups are arranged at adistance d from the scale device. The detector groups are adjacentlyarranged at a distance δ from each other. The distance δ is arranged tobe larger than the gap distance a, i.e., distance covered by the gap,such that one of the detector groups always is positioned outside thegap 340. The scale device is a magnetic scale device such as a magneticencoding tape having a number of equidistant magnetic poles in the formof alternating north and south poles. Each pair of successive north andsouth poles together form a wavelength λ.

According to example embodiments, both the first detector group 50:1 andthe second detector group 50:2 are arranged to continuously generate atleast one output signal in the form of signal pairs signal pair A1B1 andsignal pair A2B2 respectively to a signal processing device, such as thesignal processing described with reference to FIGS. 2 and/or 5. Inresponse to receiving the at least one output signal from the twodetector groups, the signal processing device is arranged to determinewhich of the signal pairs A1B1 and A2B2 to use as basis for generatingan estimated position signal to be presented to an output, such as theoutput signal generation device described with reference to FIG. 5. Inorder to determine which of the detector groups to use as basis forestimating a position signal, information relating to direction ofmovement of the scale device relative the detector groups, as determinedby the phase difference between the signals within at least one of firstand second signal pairs A1B1, A2B2 is used. In more detail, the sequencein which the detector groups pass the gap is used to determine which ofthe detector groups to use as basis for estimating a position signal, inwhich the sequence in which the detector groups pass the gap isdetermined by the direction of movement of the scale device. As adefault, the detector group determined to be second in sequence to passthe gap is used as basis for generating a position estimation signal.When the detector group first in sequence to pass the gap has passed theentire distance of the gap a switch is made from using the detectorgroup second in sequence to pass the gap, i.e., from the detector groupnot having passed the gap to using detector group first in sequence topass the gap, i.e., the detector group having passed the entire distanceof the gap. When the detector group second in sequence to pass the gaphas passed the entire distance of the gap a switch from the detectorgroup first in sequence to pass the gap to the detector group second insequence to pass the gap is performed.

As an example with further reference to FIG. 8B, the first and seconddetector groups is connected to a stationary part of the measurementobject so that the detector groups remains stationary. The scale devicein the form of at least two sections 35:1, 35:2 of the scale device isattached to a moving part of the measurement object, such ascircumferentially attached to a shaft as illustrated in FIG. 1, 7A or8A, so that the scale device moves together with the moving part of themeasurement object. This means that the scale device moves relative tothe detector groups whereby the detector groups is configured todetermine a position of the moving part of the measurement object basedon sensing the movement of the scale device. In this example, the scaledevice in the form of two sections 35:1, 35:2 moves in a direction Z. Inorder to sense the movement of the scale device, each of the detectorgroups includes at least two magnetic sensors, such as at least two MRsensors, operable to sense changes in magnetic field generated by themoving scale device in the form of a magnetic scale device, including aplurality of equidistant magnetic north and south poles. The magneticnorth and south poles are arranged in an alternating pattern along theextension of the scale device.

Since the gap of the scale device includes no scale marking elements,e.g., magnetic north and south poles, a detector group positioned abovethe gap will not be able to generate an output signal suitable for useas basis for generating a position estimation signal. However, since atleast one of the first and second detector groups always is positionedabove the scale device outside the gap, at least one of the first andsecond detector groups will always produce a signal suitable to use asbasis for generating a position estimation signal.

In this example, in case none of the detector groups have passed thegap, the first detector group will pass over the gap before the seconddetector group will pass over the gap. In more detail, since the scaledevice in this example move in a direction Z relative to the stationarydetector groups, the first detector group will be first in sequence topass over the gap and the second detector group will be second insequence to pass over the gap.

This means that provided the movement of the scale device as indicatedby the direction Z as illustrated in FIG. 8B, the first detector groupwill lose the possibility of generating an output signal suitable foruse as basis in order to provide a position estimation when passing overthe gap.

In cases where the movement of the scale device is opposite to thedirection Z, the gap start position and gap end position will switchplace as compared to the illustrated example with reference to FIG. 8B.In more detail, the gap start position will be the gap end position asillustrated in FIG. 8B, and the gap end position will be the gap startposition as illustrated in FIG. 8B. This means that the second detectorgroup will be first in sequence to pass over the gap and that the firstdetector group will be the second in sequence to pass over the gap.

In order to determine which of the first and second detector groups thatare first and second in sequence to pass over the gap the phasedifference as explained above is used. For example, the detected phasedifference will determine if the scale device moves in the direction Zor in a direction opposite to Z.

According to example embodiments, at least one gap end position signalgenerated in response to at least one of the detector groups reaching agap end position GE. According to this example embodiment, the gap endposition signal is used to determine when to switch between the twodetector groups.

According to example embodiments, at least one gap start position signalgenerated in response to at least one of the detector groups reaching agap start position GS.

Information relating to gap distance is described below.

According to example embodiments, both at least one gap start positionsignal and at least one gap end position signal are generated. Accordingto this example embodiment, both the at least one gap start signal andthe at least one gap end signal is used to determine when to switchbetween the two detector groups.

According to example embodiments, information relating to gap position,i.e., information defining where on the scale device the gap ispositioned is used to determine when to switch between the two detectorgroups. The gap position information may be predetermined or determinedduring a first gap passage.

Handling of stop/switch of direction when a detector group is positionedabove the gap is described below.

FIG. 8C is a block diagram illustrating another example embodiment 90Dof the system 90 for detecting movement and/or position of a rotatableshaft, such as the shaft 20 of FIG. 1.

FIG. 8D is a block diagram illustrating another example embodiment 90Eof the system 90 for detecting movement and/or position of a rotatableshaft, such as the shaft 20 of FIG. 1.

FIG. 9A is an illustration showing how gap detection is performed by theencoder system.

As shown in FIG. 9A, two signals αA, αB in the form of processed outputsignals from the first and second detector groups are generated. Thesignals αA, αB correspond to processed signals from the first and seconddetector groups 50:1 and 50:2, in which αA is the signal resulting fromprocessing the output of the first detector group 50:1 and αB is thesignal resulting from processing the output of the second detector group50:2.

ε denotes a threshold level for determining a deviation corresponding toa detected gap. In example embodiments, ε is determined to be half thelength of the gap, e.g., half the length a of the gap 340 as describedwith reference to FIG. 8B.

FIG. 9B is an illustration showing an implementation of synchronizationassociated to switching between the two detector groups.

As shown in FIG. 9B, switching takes place two times for each gappassage.

P1A denotes a position in which the first detector group passes over agap. P1B denotes a position wherein the first detector group has passedthe gap.

P2A denotes a position wherein the second detector group passes over agap. P2B denotes a position wherein the second detector group has passedthe gap.

FIG. 9C is an illustration showing an implementation of synchronizationassociated to switching between the two detector groups.

It is sometimes desirable to generate a reference pulse, at least onceper shaft revolution, so that it indicates an absolute position of theshaft 20 with a very small degree of inaccuracy. However, at least someportions of the length of a scale device 30 being attached on a shaftmay “float” in relation to the shaft, e.g., as a result of temperaturefluctuations. Hence, unfortunately, if the reference pulse is generatedin direct dependence on a position of the scale device 30 that “floats,”the position indicated by that reference pulse may also “float” inrelation to the shaft, rendering a somewhat less accurate positionindication.

FIG. 10A is an illustration showing an implementation of a generation ofa reference pulse according to an example embodiment of the presentinvention.

As shown in FIG. 10A, at least one fastening element F1, such as ascrew, is used to firmly attach the scale device 30 to the measurementobject 20 at a position FP of the scale device 30.

According to example embodiments, at least one fixpoint position FP maybe implemented. The fixpoint is used as a fixed reference position toindicate a reference position on the scale device. The referenceposition may be used to generate one reference pulse per revolution ofthe measurement object. Accordingly, whenever a reference pulse may begenerated indicating that the measurement object is known to be at aparticular position relative the detector groups.

By implementing a fixpoint it is possible to generate a referencepulse/null pulse once per shaft revolution so that the shaft positionindicated by the reference pulse truly indicates the actual position ofthe shaft, despite the fact that parts of the scale device/ring 30 will“float” in relation to the shaft in dependence on temperaturevariations.

The fixpoint may, for example, be a position and/portion of the scaledevice, where the scale device is firmly coupled to the measurementobject. As an example, the fixpoint may be a point FP and/or region FPRof the scale device located at and/or near a fastening element F1securing the scale device to the measurement object. For example, thefixpoint may be positioned near and/or at a fastening element F1 such asa screw other suitable fastening element F1, arranged to fasten thescale device to the measurement object.

The fixpoint or fixpoint region is located at a predetermined distanceFPOFFSET from a gap 340.

FIG. 10B is an illustration showing an implementation of a generation ofa reference pulse, based on using the fixpoint, such as described withreference to FIG. 10A, according an example embodiment of the presentinvention.

FIG. 11 is an illustration showing a flow chart of a method forgenerating a reference pulse according to an example embodiment of thepresent invention.

According to example embodiments, a method for generating a referencepulse using a fixpoint, such as described with reference to FIG. 10A, isprovided. The reference pulse may, for example, be used one pulse, e.g.,reference pulse, per revolution of the measurement object and may thusprovide information indicative of the number of revolutions and theposition of the measurement object. Accordingly, whenever a referencepulse is generated i.e., whenever the fixpoint is reached, themeasurement object, such as a shaft, is known to be at a particularabsolute position relative the detector groups.

According to example embodiments, there is provided an initiation methodfor setting fixpoint parameters.

Once the initiation method has been performed, the encoder, soinitiated, will be able to perform a method for repeatedly generating areference pulse so that the shaft position indicated by the referencepulse truly indicates the actual position of the shaft, despite the factthat parts of the scale device/ring 30 will “float” in relation to theshaft in dependence on temperature variations.

As the shaft rotates, the encoder will generate at least one scale gapindicator signal in dependence of the detection of a gap in the scale,as described herein. According to example embodiments, the analyzer isadapted to generate the scale gap indicator signal in response to thedifference value (e) reaching a predetermined value, the predeterminedvalue being substantially half of the gap width value. The differencevalue (e), according to this example embodiment, is generated by adeviation between the estimates Zest2 and Zest1.

However, the fixpoint procedure may rely on a scale gap indicator signalgenerated in other manners, as described herein.

The initiation method may include the following steps:

S200: Decide to use a selected one of the scale gap indicator signalsthat the encoder may be capable of generating.

S210: Measure or set into a memory location, an offset value FPOFFSET(see FIG. 10A), the offset value being indicative of a distance, interms of first predetermined wavelengths λ₁, from the position of thescale device where the selected scale gap indicator signal is generated.According to example embodiments, the selected scale gap indicatorsignal may be generated in response to a midpoint of the gap 340, asillustrated in FIG. 10A.

S220: Identify an amplitude value FP in the signal S_(EA1) as generatedby the arctan function generator module 260:1 (see FIG. 10B inconjunction with FIG. 7C), at a position Z which is located at thedistance of offset value FPOFFSET from the position where the scale gapindicator signal is generated.

S230: The amplitude value of the signal S_(EA1) at that position FP isstored as a reference amplitude value A_(FP). Since this amplitude valueA_(FP) is generated at a position near the fastening element F1, we cantrust that the pole elements 120 (See FIGS. 3 a, B, and C) near thefastening element F1 will be firmly attached to the shaft 20. Hence,that position FP of the scale device will always truly correspond to theposition FP of the shaft. Moreover, the precise amplitude value A_(FP)is generated only once per first predetermined wavelength λ₁ of thesignal S_(EA1). Hence, once a precise amplitude value A_(FP) has beenstored, that amplitude value A_(FP) may be used to trigger a referencepulse.

Once the above initiation method has been performed, the followingmethod may be used for generating a reference pulse.

S310: As the shaft rotates, the scale device rotates and the selectedscale gap indicator signal will occur once per revolution.

S320: A distance meter is started in response to the reception of theselected scale gap indicator signal.

Although this selected scale gap indicator signal will keep occurringonce per revolution, thereby being quite sufficiently accurate forindicating, e.g., the average speed of rotation of the shaft 20, theportion of the scale device 30 generating the scale gap indicator signalmay not be firmly attached to the shaft. However, the position of thescale gap indicator signal is sufficiently accurate as a starting pointso at to find an area FP_(A) within half a first predeterminedwavelength λ₁ from the position FP.

S330: As the shaft rotates, the distance meter provides a measure of thedistance since the latest occurrence of the selected scale gap indicatorsignal.

S340: When the distance meter indicates the distance of about FPOFFSETfrom the latest occurrence of the selected scale gap indicator signal,the encoder may be adapted to compare the current value of the signalS_(EA1) generated by the arctan function generator module 260:1 (seeFIG. 10B in conjunction with FIG. 7C) with the stored referenceamplitude value A_(FP).

S350: When the current value of the signal S_(EA1) equals the storedreference amplitude value A_(FP), the encoder is adapted to generate afix point reference signal.

The output signal generator of the encoder may be adapted to generate anencoder output reference signal in direct response to the fix pointreference signal.

Hence, the fix point reference signal may be generated in response tothe detection of a previously stored reference amplitude value A_(FP).Since that particular amplitude value is unique within the distance ofone first predetermined wavelength λ₁ as illustrated by FIG. 10B, andsince the physical portion FP of the scale device 30 is firmly attachedto the shaft by a fastener F1 (See FIG. 10A), the shaft position atwhich the fix point reference signal is generated will have a smalldegree of inaccuracy.

In a first method step S100, a distance FPOFFSET from a gap to afixpoint position FP or the distance FPOFFSET from a gap to a positionwithin a fixpoint region FPR is stored.

After the method step S100, a subsequent method step S110 is performed.

In the method step S110, a gap in the scale device is detected.

After the method step S110, a subsequent method step S120 is performed.

In the method step S120, it is determined when the position of thefixpoint or the position within the fixpoint regions is reached. Forexample, the distance FPOFFSET indicative of the distance between thegap and the fixpoint position or position within the fixpoint region isused to determine when the position of the fixpoint or the positionwithin the fixpoint region is reached.

After the method step S120, a subsequent method step S130 is performed.

In the method step S130, an electrical angle at the fixpoint position oran electrical angle at the position within the fixpoint region isstored. For example, when the position of the fixpoint or when theposition within the fixpoint region is reached by at least one of thedetector groups 50:1, 50:2, one of the signal pairs A1B1 and A2B2 isprocessed by using the arctan function to determine the electrical angleat the fixpoint position or at the position within the fixpoint region.The electrical angle is subsequently stored in a memory deviceassociated with the encoder system, such as a flash memory device.

After the method step S130, a subsequent method step S140 is performed.

In the method step S140, a reference pulse is generated at the positionof the fixpoint or at the position within the fixpoint region.

After the method step S140, a subsequent method step S150 is performed.

In the method step S150, a gap is detected. For example, it is detectedwhen the gap is reached at least a second time as a result of therevolutions of the measurement object.

After the method step S150, a subsequent method step S160 is performed.

In the method step S160, it is detected when a tolerance window of thefixpoint position or when a tolerance window of the position within thefixpoint region is reached. For example, it is detected when apredetermined tolerance window of the fixpoint position or when apredetermined tolerance window of the position within the fixpointregion is reached. The predetermined tolerance window may, for example,correspond to −λ/2 to λ/2 as described with reference to FIG. 10A.

After the method step S160, a subsequent method step S170 is performed.

In the method step S170, it is determined when the stored electricalangle is reached. In other words, when the electrical angle within thetolerance window corresponds to the stored electrical angle. Forexample, when the tolerance window is reached, it is determined when thestored electrical angle is reached by processing the arctan function ofat least one of the signal pairs A1B1, A2B2, generated by the detectorgroups 50:1, 50:2.

After the method step S170, a subsequent method step S180 is performed.

In the method step S180, a reference pulse is generated. For example, areference pulse is generated in response to the stored electrical anglebeing reached within the tolerance window.

After the method step S180, the method may end or repeat from step S150to provide for generation of subsequent reference pulses in response torevolutions of the measurement object.

What is claimed is:
 1. An encoder for detection of rotational movementof a rotatable shaft in relation to a part of a machine, comprising: ascale device adapted to attach to a circumference of the shaft, thescale device having a width and a length and including a first magneticscale pattern having a plurality of magnetic pole elements provided witha first predetermined division in a direction of the length adapted togenerate a first magnetic field pattern at a first distance from asurface of the scale device, the scale device including at least one gapbetween ends of the first magnetic scale pattern; and a signal generatoradapted to mount on the machine part, the signal generator including: ahousing; a first output terminal adapted to provide an encoder outputsignal indicative of a relative change in position between the signalgenerator and the scale device; a second output terminal adapted toprovide a reference signal indicative of a rotational position of theshaft; a first magneto-electric transducer head having a firstmagneto-electric transducer adapted to generate a first electric signalin response to detection of the magnetic field pattern so that the firstelectric signal varies periodically in dependence on the first magneticfield pattern such that the variation exhibits a first wavelength thatdepends on the first predetermined division when the firstmagneto-electric transducer moves along the first magnetic scalepattern; a second magneto-electric transducer head having a secondmagneto-electric transducer adapted to generate a second electric signalin response to detection of the first magnetic field pattern so that thesecond electric signal varies periodically in dependence on the firstmagnetic field pattern such that the variation exhibits the firstwavelength dependent on the first predetermined division when the secondmagneto-electric transducer moves along the first magnetic scalepattern; a first signal processing unit including: a first deviceadapted to generate a periodically varying first digital signal independence on the first electric signal such that the variation of thefirst digital signal exhibits the first wavelength when the firstmagneto-electric transducer moves along the first magnetic scalepattern; and a second device adapted to generate a periodically varyingsecond digital signal in dependence on the second electric signal suchthat the variation of the second digital signal exhibits the firstwavelength when the second magneto-electric transducer moves along thefirst magnetic scale pattern (35, 140); an analyzer adapted to generatea scale gap indicator signal in dependence on detection of the gap; andan output signal producer adapted to produce the encoder output signalin dependence on the first digital signal and the second digital signaland adapted to produce the reference signal in dependence on the scalegap indicator signal.
 2. The encoder according claim 1, wherein theanalyzer is adapted to generate the scale gap indicator signal independence on an analysis involving the first digital signal, ananalysis involving the second digital signal, and/or a comparativeanalysis involving the first digital signal and the second digitalsignal.
 3. The encoder according claim 1, wherein the analyzer isadapted to generate the scale gap indicator signal: (a) in response todetection of a deviation between the magnetic field pattern as sensed bythe first magneto-electric transducer head and the magnetic fieldpattern sensed by the second magneto-electric transducer head; and/or(b) in response to detection of a change in: (i) the magnetic fieldpattern as sensed by the first magneto-electric transducer head; or (ii)the magnetic field pattern sensed by the second magneto-electrictransducer head.
 4. The encoder according claim 1, wherein the analyzeris adapted to generate the scale gap indicator signal in response todetection of a change in: (a) the magnetic field pattern as sensed bythe first magneto-electric transducer head by a phase error signalswitching from a state indicating no phase error to a state indicatingdetection of a phase error; and/or (b) the magnetic field pattern assensed by the first magneto-electric transducer head by a phase errorsignal switching from a state indicating a phase error to a stateindicating no phase error.
 5. The encoder according claim 1, wherein theanalyzer is adapted to generate the scale gap indicator signal independence on a comparative analysis involving a first position valueestimate and a second position value estimate.
 6. The encoder accordingclaim 1, the analyzer is adapted to generate a First_off_Scale signalindicating that the first magneto-electric transducer head is not in aposition to detect the scale when a second position value estimateindicates a certain degree of movement and a first position valueestimate indicates less movement or substantially no movement, andwherein the analyzer is adapted to generate the scale gap indicatorsignal in response to the First_off_Scale signal.
 7. The encoderaccording claim 1, wherein the said analyzer is adapted to generate avalue indicative of a difference in detected movement, the differencevalue indicating a difference between a second position value estimateand a first position value estimate.
 8. The encoder according to claim7, wherein the analyzer is adapted to generate the scale gap indicatorsignal in response to the difference value reaching a predeterminedvalue.
 9. The encoder according claim 7, wherein the analyzer is adaptedto generate the scale gap indicator signal in response to the differencevalue reaching a predetermined value corresponding to a certain ratio ofa gap width value.
 10. The encoder according claim 7, wherein theanalyzer is adapted to generate the scale gap indicator signal inresponse to the difference value reaching a predetermined value beingsubstantially half of a gap width value.
 11. The encoder according claim1, wherein the first magneto-electric transducer head includes a firstlagged magneto-electric transducer adapted to generate a first laggedelectric signal in response to detection of the magnetic field patternso that the first lagged electric signal varies periodically independence on the magnetic field pattern such that the variationexhibits the first wavelength that depends on the first predetermineddivision when the first lagged magneto-electric transducer moves alongthe magnetic scale pattern; wherein the first lagged magneto-electrictransducer is positioned in relation to the first transducer such that,in operation, the first lagged electric signal varies at a first lag inrelation to the first electric signal when the shaft rotates in aclockwise rotational direction, and such that the first lagged electricsignal varies at a second lag in relation to the first electric signalwhen the shaft rotates in a counterclockwise rotational direction, thesecond lag being different from the first lag; wherein the first deviceis adapted to also generate a periodically varying first lagged digitalsignal such that, in operation, the first lagged digital signal variesat a first lag in relation to the first digital signal when the shaftrotates in a clockwise rotational direction, and such that the firstlagged electric signal varies at a second lag in relation to the firstelectric signal when the shaft rotates in a counterclockwise rotationaldirection, the second lag being different from the first lag; andwherein the analyzer is adapted to generate the scale gap indicatorsignal in dependence on an amplitude analysis of the periodicallyvarying first digital signal and the periodically varying first laggeddigital signal in accordance with the periodically varying first digitalsignal and the periodically varying first lagged digital signal beingsubstantially quadrature signals when the first magneto-electrictransducer moves along a first magnetic scale pattern.
 12. The encoderaccording to claim 11, wherein the second magneto-electric transducerhead includes a second lagged magneto-electric transducer adapted togenerate a second lagged electric signal in response to detection of themagnetic field pattern so that the second lagged electric signal variesperiodically in dependence on the magnetic field pattern such that thevariation exhibits the first wavelength that depends on the firstpredetermined division when the second lagged magneto-electrictransducer moves along the magnetic scale pattern; wherein the secondlagged magneto-electric transducer is positioned in relation to thesecond transducer such that, in operation, the second lagged electricsignal varies at a first lag in relation to the second electric signalwhen the shaft rotates in a clockwise rotational direction, and suchthat the second lagged electric signal varies at a second lag inrelation to the second electric signal when the shaft rotates in acounterclockwise rotational direction; wherein the second device isadapted to also generate a periodically varying second lagged digitalsignal such that, in operation, the second lagged digital signal variesat a first lag in relation to the second digital signal when the shaftrotates in a clockwise rotational direction, and such that the secondlagged digital signal varies at a second lag in relation to the seconddigital signal when the shaft rotates in a counterclockwise rotationaldirection; and wherein the analyzer is adapted to generate the scale gapindicator signal in dependence on an amplitude analysis of theperiodically varying second digital signal and the periodically varyingsecond lagged digital signal in accordance with the periodically varyingsecond digital signal and the periodically varying second lagged digitalsignal being substantially quadrature signals when the firstmagneto-electric transducer moves along a first magnetic scale pattern.13. The encoder according to claim 12, wherein the analyzer is adaptedto set a first amplitude reference value in dependence on a sum of asquare of the periodically varying first digital signal and a square ofthe periodically varying first lagged digital signal; wherein theanalyzer is adapted to set a second amplitude reference value independence on a sum of a square of the periodically varying seconddigital signal and the periodically varying second lagged digitalsignal; and wherein the analyzer is adapted to generate the scale gapindicator signal in dependence on a relation between the first amplitudereference value and the second amplitude reference value.
 14. Theencoder according to claim 1, further comprising an encoder userinterface adapted to allow a user to select use of a selectable scalegap indicator signal; wherein the encoder allows for setting of anoffset parameter value that is indicative of a distance from a positionof the scale device where the selected scale gap indicator signal isgenerated to a position of the scale device that may be firmly attachedto the shaft; wherein the encoder is adapted to identify a referenceamplitude value in a signal generated by an arctan function generatormodule, the reference amplitude value occurring at a position located ata distance substantially corresponding to the offset parameter valuefrom the position at which the selected scale gap indicator signal isgenerated; and wherein the encoder is adapted to store the referenceamplitude value.
 15. An encoder for detection of rotational movement ofa rotatable shaft in relation to a part of a machine, comprising: ascale device adapted to attach to a circumference of the shaft, thescale device having a width and a measuring path length and including afirst magnetic scale pattern having a plurality of magnetic poleelements provided with a first predetermined division in a direction ofthe length so as to generate a first magnetic field pattern at a firstdistance from a surface of the scale device, the scale device includingat least one gap between ends of the first magnetic scale pattern; asignal generator adapted to mount on the machine part and including: ahousing; a first output terminal adapted to provide an encoder outputsignal indicative of a relative change in position between the signalgenerator and the scale device; a first magneto-electric transducer headhaving a first magneto-electric transducer adapted to generate a firstelectric signal in response to detection of the first magnetic fieldpattern so that the first electric signal varies periodically independence on the first magnetic field pattern such that the variationexhibits a first wavelength that depends on the first predetermineddivision when the first magneto-electric transducer moves along thefirst magnetic scale pattern; a second magneto-electric transducer headhaving a second magneto-electric transducer adapted to generate a secondelectric signal in response to detection of the first magnetic fieldpattern so that the second electric signal varies periodically independence on the first magnetic field pattern such that the variationexhibits the first wavelength dependent on the first predetermineddivision when the second magneto-electric transducer moves along thefirst magnetic scale pattern; a first signal processing unit including:a first device adapted to generate a periodically varying first digitalsignal in dependence on the first electric signal such that thevariation of the first digital signal exhibits the first wavelength whenthe first magneto-electric transducer moves along the first magneticscale pattern; and a second device adapted to generate a periodicallyvarying second digital signal in dependence on the second electricsignal such that the variation of the second digital signal exhibits thefirst wavelength when the second magneto-electric transducer moves alongthe first magnetic scale pattern; an analyzer adapted to generate ascale gap indicator signal in dependence on detection of the gap; and anoutput signal producer adapted to produce the encoder output signal independence on the first digital signal, the second digital signal, andthe scale gap indicator signal.
 16. The encoder according claim 15,wherein the analyzer is adapted to generate the scale gap indicatorsignal in dependence on an analysis involving the first digital signal,an analysis involving the second digital signal, and/or a comparativeanalysis involving the first digital signal and the second digitalsignal.
 17. The encoder according claim 15, wherein the analyzer isadapted to generate the scale gap indicator signal: (a) in response todetection of a deviation between the magnetic field pattern as sensed bythe first magneto-electric transducer head and the magnetic fieldpattern sensed by the second magneto-electric transducer head; and/or(b) in response to detection of a change in: (i) the magnetic fieldpattern as sensed by the first magneto-electric transducer head; or (ii)the magnetic field pattern sensed by the second magneto-electrictransducer head.
 18. The encoder according claim 15, wherein theanalyzer is adapted to generate the scale gap indicator signal inresponse to detection of a change in: (a) the magnetic field pattern assensed by the first magneto-electric transducer head by a phase errorsignal switching from a state indicating no phase error to a stateindicating detection of a phase error; and/or (b) the magnetic fieldpattern as sensed by the first magneto-electric transducer head by aphase error signal switching from a state indicating a phase error to astate indicating no phase error.